Last updated: 180901, … 240624  (Most current version as PDF)

I abandoned using Surprise as written years ago—so long ago I don’t recall why. I suspect because I tried to make the rules make sense, and as written they don’t (and can’t, there are errors in the early printings of the PHB and DMG!). The rules are also surprisingly (hah!) unclear on who rolls for what effect. Am I rolling for whether I’m surprising or surprised? What if the result is modified?

 I’ve recently been inspired to dig into some of the more fiddly AD&D rules, and have been impressed at how well those rules work once I understand them, so I thought I’d try Surprise again. That said, I’ve modified the below just a bit to be consistent with the rest of my house rules (see Initiative). I limit surprise to a single attack per segment, without stacking, to a maximum of 2 attacks. That’s intentional, otherwise 7th level Elven Ranger catching someone completely flat-footed could gain 10 melee attacks during Surprise (and more extreme examples exist!)

A surprised party is one caught unawares or unprepared by another party (DMG, p. 61, 62). In such circumstances the non-surprised (or less surprised) party has an advantage of “free and unanswered activity to move, attack, flee, etc.,” reflected by free segments of actions against the surprised party prior to rolling initiative. It is possible for both parties to be surprised equally—with Surprise thus having no effect.  Parties are unaware of how surprised the other side is.

Prior detection negates the possibility of being surprised. Light can spoil the possibility of surprise for one party. Noise can negate surprise considerations, whether the sound is the normal progress of the party or a fruitless attempt to open a door. A party hearing something at a door (Hear Noise) negates their possibility of surprise. Magical devices can possibly negate surprise by detection of thoughts or intentions. In all such cases, only parties subject to surprise roll to determine surprise (DMG, p. 62). If one party is making considerable noise which is discernible by the other party, the latter will also have the options of fleeing or concealment regardless of Surprise; the former negating the encounter, the latter allowing distance to be 1″ to 4″ before discovery by the noisy party (DMG, p. 62).

For each side, if the chance of surprise exists, a single d6 is rolled to determine whether their entire side is surprised. By default, on a 1 or 2 their side is surprised, for the number of segments equal to the number rolled on the die, otherwise (on 3-6) they are not surprised. If a creature surprises on 4 in 6, it can surprise for up to 4 segments (when their opponent rolls 1-4 on a d6) (PHB, p. 51,103; DMG, p. 62).

If both parties roll results in their range for Surprise, Surprise duration is calculated for one party based on the net of the two Surprise results: “Assume A [surprised on 5 in 6] rolls a 4, so A is surprised for 4 segments unless B rolls a 1, in which case A’s inactive period will be only 3 segments, or if B rolls a 2, in which case A’s surprise will last for only 2 segments (4–1 = 3, 4–2 = 2).” (DMG, p. 62). Only one side will have lost segments (DMG, p. 61, PHB, p. 103). Subtract the segments of surprise from each other, not the dice rolls. Only the non-surprised party can act.

“Complete Surprise” is defined as 2 (or more) segments of surprise [c.f. , MM-Catoblepas; DMG-Crossbow of Speed; PHB-Phantasmal Killer; UA-garrote; MM2-Dracolisk; G1-3, p.12 & 23; S3, p. 13 & 14; and the potential 4 segments of surprise for the Aerial Servant (PHB/MM). See Eldrich Wizardry, p.10 for origins of Complete Surprise. The Boalisk prompts “Complete Surprise” on a 1-2; whether the Boalisk rolls a 1 or 2, it will surprise for 2 segments. [I choose to interpret that any surprise ≥ 2 segments is “Complete Surprise” of 2 segments.]

Only once Surprise is completely resolved do both parties roll Initiative.

 

Encounter Distance

If either or both parties are surprised, the normal underground encounter distance of d6+4″ will typically be only 1″ to 3″, as surprise is normally a factor only in close encounter/underground situations. When outdoors, each segment of surprise reduces the normal encounter distance (6d4″) by 1″ (DMG, p. 49) in addition to free segments of activity. Terrain type will also modify encounter distance:

Scrub	-1 per distance die on all 3’s and 4’s.
Forest	-1 per distance die on all numbers (00’s are possible).
Marsh	-1 per distance die on all 2’s, 3’s, and 4’s.

 

Illumination or visual capability of the concerned parties also affects encounter distance. A light source reliance limits the encounter distance to twice the normal vision radius of the source (2× radius of the light source). lnfravision and/or ultravision operate only to the stated limit of their range and limit encounter distance accordingly (DMG, p. 62).

Interpretation: What if, due to prior detection, Party A is surprised but the Party B is not? Determine the normal encounter distance for Party B. Should Party B not react, encounter distance can be determined as normal for Surprise (d3″), otherwise Party B has the number of Surprise segments to react from the normal encounter distance. This contradicts the DMG (p. 62): “If either or both parties are surprised, the distance must be either 1″ to 3″ or it must be less as determined under the actual area modifier.” but takes into account the exception of prior detection (light, noise).

Modifiers to the Chance of Being Surprised (Your Die)

Audial or visual superiority will tend to negate surprise (DMG, p. 194). A party (or group of monsters) is surprised only as easily as its most perceptive member if that awareness can be communicated; e.g., in a party with a ranger (surprised only on 1 in 6), the entire party is only surprised on a 1 in d6 (DMG, p. 61). If awareness is limited (such as a human ranger in the dark), special class or race benefits do not apply (WSG, p. 13, DSG, p. 60).

In the case where the party is surprised on 1 in d6, the overall chance to be surprised is reduced by 1. In this case if the other side would normally surprise 5 in d6, the net result is the party will be surprised only on 4 in d6 (DMG, p. 62)—not Surprised on 5 in d6, and then the duration reduced by 1 segment.

The Rod of Alertness (UA, p. 94) “bestows +1 to the possessor’s die rolls for being surprised”. While it might appear this creates additional segments of surprise, it does not. A normal PC is surprised on 1-2 in d6: a 1 in 6 chance of being surprised 1 segment (if a 1 is rolled), and a 1 in 6 chance of being surprised for 2 segments (if a 2 is rolled). After adding a +1 to the die, the chance of being surprised 2 segments is the same (1 in 6, if a 1 + 1 is rolled), but it’s no longer possible to be surprised 1 segment.

Alertness/Senses can make a party or individual less susceptible to surprise:

• Alertness makes the ettin difficult to surprise (decreasing the Surprise range by 1 to 1 in d6 instead of 1-2 in d6) due to their alertness (MM, p. 20).
• All cloud giants have a keen sense of smell, thus they are surprised only a 1 in d6 (decreasing the Surprise range by 1 to 1 in d6 instead of 1-2 in d6) due to their alertness (MM, p. 44).
• Hell hounds have keen hearing, and they are surprised on a die roll of 1 in d6) (decreasing the Surprise range by 1 to 1 in d6 instead of 1-2 in d6) due to their alertness) (MM, p. 51).
• Satyrs have keen senses, so are surprised only on a 1 (decreasing the Surprise range by 1 to 1 in d6 instead of 1-2 in d6) due to their alertness (MM, p. 85).
• The keen hearing and eyesight of giant apes makes them only surprised on a 1 (decreasing the Surprise range by 1 to 1 in d6 instead of 1-2 in d6) due to their alertness (MM, p. 7).
• The unusual peripheral vision of the kna, kopru, and shark decreases their Surprise range by 1 to 1 in d6 instead of 1-2 in d6 (PC3, p. 3).
• Rangers (& Duelists) are surprised only on 1 in d6 (decreasing the surprise range by 1, normally to 1 in d6 instead of 1-2 in d6) due to their alertness (Polyhedron #12, p. 10). [The Ranger ability originally derived from their tracking.⁴]
• Barbarians are surprised only on 1 in d10 (effectively decreasing the normal range by 4 from 2 in d6 to 1 in d10 (see Calculating Cumulative Surprise below) due to their alertness. This further decreases the normal range by an additional 2 (to 1 in 20) if in familiar terrain. [I find this overpowering at a party level, and instead consider the Barbarian ability as identical to the Ranger ability. That also removes a recurring Surprise d10 complication.]
• With a proficiency check, characters with Alertness decrease the range by 1, now 1 in d6 instead of 1-2 in d6. Assuming an ability to communicate to others in the party, their chance of being surprised is also reduced by that amount. Otherwise treat the number of segments they are surprised as reduced by 1. Interpretation: This does not stack with the class abilities that reduce the chance of being surprised—those classes effectively have this proficiency without the requirement for a proficiency slot or proficiency check.

Interpretation: A few creatures with exceptional senses are defined as unable to be Surprised (Brownies with “exceptional senses”, barbed devils “alert at all times”, eagles “eyesight”, leprechaun’s “keen ears”. Exceptional senses could be calculated as an additional -1 from Surprise for extreme sensory capacity (considered as surprised 0 in 6 prior to other adjustments). Keen senses can be interpreted as being twice as good (seeing or hearing twice as far).

 

Modifiers to the Chance of Surprising Others (Their Die)

Surprise capability relates to special movement ability and possibly other factors (DMG, p. 194). A party with an increased chance to surprise their opponents increases their opponents’ range from 1-2 in d6 to 1-3 or more (also increasing the potential number of segments that their opponent(s) can be surprised), but only if that increased chance of surprise is true for the entire party (e.g., all rangers, a group of only halflings and elves 90’ in advance not wearing armor, all huge spiders, etc.).

Rolls that adjust the Surprise roll (such as Hide in Shadows, Move Silently, or Boots of Elvenkind) must be checked prior to a Surprise roll, as success can indicate an improved chance to surprise an opponent (PHB, p. 102, 103).

• Noise can negate surprise considerations, whether the sound is the normal progress of the party or a failed attempt to open a door. Characters in metal armor can be heard for 90′, hard boots can be heard at 60′, and relatively quiet movement can be heard at 30′ (DMG, p. 68).
• Being hidden (invisibility, camouflage, hiding in shadows) increases the opponents’ chance of being surprised by 1 (increasing the opponents’ range by 1, e.g. surprised on 1-3 in d6 instead of 1-2 in d6) (PHB, p. 103; Drmg #133; FF, p. 17, Bullywug). One cannot Hide in Shadows and Move (Silently) (DMG, p. 19, PHB, p. 28).
• Move Silently/Silence increases the opponents’ chance of being surprised by 1 (increasing the opponents’ range by 1, e.g. surprised on 1-3 in d6 instead of 1-2 in d6) due to stealth (PHB, p. 103, Drmg#133). One cannot Hide in Shadows and Move (Silently) (DMG, p. 19, PHB, p. 28). Bugbears and undead are explicitly silent (DMG, p. 60), also increasing the opponents’ chance of being surprised by 1. Hell hounds “move with great stealth”, granting them the ability to surprise on 1-4 in d6 (MM, p. 51).
• Psionic invisibility is a mind control ability (“The Shadow Knows!”) which is more similar to the druidic Invisibility to Animals, for the affected creature(s) does not notice sounds or odors from the psionic (DMG, p. 60), increasing the opponents’ range by 2 (1-4 in d6) due to being hidden and silent.
• Elves and Halflings surprise opponents 1-4 in d6 when not in metal armor and 90’ in advance (increasing their opponents’ range by 2, e.g. surprised on 1-4 in d6 instead of 1-2 in d6), due to both their stealth and ability to be hidden. If they open a portal, that chance for surprise returns to 1-2 in d6. See also Solonor (UA, p. 113).
• Metal armor is not a factor for rangers, clarifying that the ranger Surprise benefit isn’t due to silence. Rangers surprise opponents 50% of the time (increasing their opponent’s chance of being surprised by 1, e.g. surprised on 1-3 in d6 instead of 1-2 in d6 (Polyhedron #12, p. 10) due to their ability to hide. This ability doesn’t explicitly include conditions, but rangers can’t surprise opponents aware of their companions and thus require the same distance as elves and halflings—rangers must be at least 90’ in advance.
• Metal armor is not a factor for barbarians when calculating Surprise, clarifying that the barbarian Surprise benefit isn’t due to silence. Barbarians increase their opponents’ chance of being surprised by 1 (increasing their opponents range by 1, e.g. surprised on 1-3 in d6 instead of 1-2 in d6) due to their ability to hide, with an additional 1-point increase if also in familiar terrain (e.g. surprised on 1-4 in d6 instead of 1-2 in d6), due to the barbarian’s ability to hide in known terrain. The barbarian’s ability doesn’t include conditions, but barbarians can’t surprise opponents aware of their companions and thus require the same distance as elves, halflings, and rangers—they must be at least 90’ in advance.
• The bullywug, when camouflaged, can further increase the chance of surprise by 2 by hopping 3″ to the attack.

 

Modifiers are cumulative when dissimilar. Example: A lone invisible elf not wearing metal armor comes upon an orc. The standard chance of being surprised is 1-2 in d6. For the orc, its range is increased due to the elf (+2 from being hidden and silent), but not further increased due to the elf’s invisibility (+1) as the elf is already hidden—the orc will be surprised if it rolls 1-4 in d6.

If both parties determine results in their range for Surprise, Surprise segments are calculated based on the difference of the resulting segments of Surprise. After rolling Surprise, the elf is surprised for 2 segments, and the orc is surprised for 4 segments—The end result is the orc is surprised for 2 segments (4 segments of surprise –2 segments of surprise) before moving on to Initiative (DMG, p. 61).

Modifiers to the Duration of Individual Surprise

Individual adjustments for Dexterity and Encumbrance never create (or negate) Surprise itself; instead they subtract (or add) segments for individuals once the party is surprised.  The Dexterity Reaction/Attacking Bonus affects that many segments of surprise for that individual only, e.g. on a range of 1-2, with the group rolling a 2, a lightly-encumbered character with a 16 Dexterity (+1 Reaction/Attacking) would be affected for one less segment. If an opponent then attempts to attack them, the attack defers to the standard initiative round (DMG, pp. 62, 71).

• Encumbered (> 105# or very bulky equipment) characters are slowed greatly (PHB, p. 102); when the party is surprised the encumbered character will be affected for an additional 2 segments.
• “Very Heavy” encumbrance (#105 or bulky armor/equipment) causes a character’s reactions to be “slowed” (in a situation of surprise) (PHB, p.102). If the party is surprised, the individual is affected for an additional segment.
• “Heavy” encumbrance (70# or fairly bulky armor/equipment) defines “no bonuses” to Surprise. Dexterity and the Ranger ability to adjust the Surprise roll? Gone!
• Only lightly or unencumbered characters [reaction normal or better, (PHB p. 101) gain the Dexterity Reaction/Attacking Bonus:
  • If the Dexterity Reaction modifier reduces the Surprise segments for an individual, that individual still can’t act during Surprise even if Dexterity reduces the individual’s Surprise segments to 0 (or below). If they are attacked individually, they are up and on their guard (DMG, p. 71), so opponents will not get an attack until Initiative.
  • All armors except leather and elfin chain are fairly bulky or bulky, making the character more than lightly encumbered for purposes of Surprise.
  • Magic armor has the same encumbrance as non-magic armor. The properties of magic armor allow movement at the next higher base rate (DMG, p. 28), not with less encumbrance.
  • Large shields are bulky (see “Very Heavy”). Magical shields however are non-bulky with respect to encumbrance (DMG, p. 28).

I choose to limit surprise attacks to a single attack per segment for 2 segments.

Actions During Surprise

While the attacker’s opponent(s) is/are surprised, each surprise segment the attacker may perform the following as if it were an entire round:

• Do nothing.
• Attempt to parlay.
• Evasion is automatic if outdoors (DMG, p. 69).
• Move 1″ (and potentially close for melee).
• Prepare (i.e., drawing or setting a weapon).
• ^*Charge 2” (if close enough) and attack.
• ^*Fire missile weapons.³ If “nocked and ready” on the first segment of Surprise, add an extra missile.
• ^*Use a breath weapon (if normally possible!).
• Attempt to activate a magical device. The device could activate during Surprise. If not enough surprise segments exist to complete activation, subtract each surprise segment from the future initiative roll (2 under my 20-segment combat round).
• Hide in Shadows (if thief, assassin, or monk).
• ^*Melee or grapple (if prepared and within 1″).
• ^*Back stab (if thief or assassin and within 1″). Surprise is required to gain the damage multiplier and +4 to hit instead of the standard +2 for a rear attack.^2,6 If at the rear, strike at +4 to hit for each surprise segment. Striking from the rear also negates any shield or Dexterity bonus. The back stab damage multiplier applies for only the first segment of surprise attack (DMG, p. 74, PHB, p. 27, Polyhedron #31, p. 29).

After surprise ends, if a thief removes themself from melee such that their opponents are no longer aware of the thief’s presence, the thief could reenter combat, attempt to Move Silently behind their opponent, and back stab again. However, they can’t gain surprise as long as their opponent is aware of their location, so have only the standard rear attack bonus of +2 with no damage multiplier.

• ^*Roll on the Assassination Table (if an assassin and within 1″). See notes under back stab.
• Spells that require but a single segment can be cast in a surprise segment. Longer-casting-time spells can only be begun during the first segment of surprise (DMG, p. 61), and if not completed by the end of Surprise subtract 1 segment (2 under my 20 segment initiative system) for each surprise segment from the future initiative round.

“[M]agic spells require the proper number of segments of casting time” (PHB., p. 103). Since, during each segment, action 4.D (“cast spell”) can be attempted, the limit is the casting time. With three segments of Surprise, a spell caster could: cast a three-segment spell; move one segment and cast a two-segment spell; cast three segments of a four-segment spell; or cast three one-segment spells. The caster does not, however, know how long their opponent will be surprised when declaring actions.

• ^*Turn undead (also action 4.D), limited by failure preventing future attempts.

^*If an attacker with Surprise individually directs an attack at an opponent who for whatever reason is not surprised (e.g., a Dexterity bonus), the attack is ineffective.

Number of Melee Attacks During Surprise

The Player’s Handbook states (p. 103):

Physical attacks during surprise situations are also possible on a 1 per segment basis, whether the form is by weapon, projectile, or method intrinsic to the creature (claws, fangs, etc.).

and the DMG reads (p. 62):

the surprising party will be able to attempt telling blows during each segment of surprise as if the segment were an entire round! That is, a fighter able to attack twice during a normal round of combat will be able to do so twice during each surprise segment, so dice are rolled for hit determination accordingly. Even if distance prevents striking with weapons, the discharge of arrows, bolts or hand-hurled weapons is permissible at three times the normal rate providing the weapon/missiles are ready, otherwise at normal rates for rounds. Once surprise segments are over, melee proceeds normally on around-by-round basis.

which clarifies that the PHB “attack” is an full round’s attack sequence, not just a single attack.

Number of Missile Attacks During Surprise

“Even if distance prevents striking with weapons, the discharge of arrows, bolts or hand-hurled weapons is permissible at three times the normal rate providing the weapon/missiles are ready, otherwise at normal rates for rounds.”

The odd quirk is the tripling of fire for missile weapons “when ready”.  The key to the fire rate is whether the weapon is ready. Looking at the usage of “ready”:

“Arlanni the thief, who had her sling ready (as the player had stated previous to the encounter), fires a shot at Blastum, who is obviously a magic-user.”
“We will go down the stairs now, with weapons drawn and ready.”
“We all get ready, I’ll nock an arrow, and the magic-user will ready her magic missile spell.”

“Ready” appears to be preparing the weapon prior to the fight. In the context of missile weapons, ready specifically as an arrow nocked. So in the first surprise segment, the archer, with an arrow nocked, fires at triple their normal rate. For the second segment, missile fire is “at normal rates”. So in the second (and later) surprise segments, missile file in a segment is as normal for a round.

So why the ability to fire 6+ arrows in the first surprise segment? Well, let’s read that slightly differently. Arrows normally fire 2 × / round. Our archer, with an arrow nocked and ready, gets the benefit of firing that “ready” arrow as a bonus over and above normal (or a total rate of fire of three, which one could call “triple”).

On the first segment of surprise, an archer with an arrow nocked and ready can fire 3 arrows, then 2 / round afterwards. That’s not precisely what the text says, but looking missile fire that way makes sense and is consistent with melee combat in surprise.

But what if we insert a paragraph break there?

That is, a fighter able to attack twice during a normal round of combat will be able to do so twice during each surprise segment, so dice are rolled for hit determination accordingly.

Even if distance prevents striking with weapons, the discharge of arrows, bolts or hand-hurled weapons is permissible at three times the normal rate providing the weapon/missiles are ready, otherwise at normal rates for rounds. Once surprise segments are over, melee proceeds normally on around-by-round basis.

The normal rate of missile fire is twice per round— 2 arrow every 10 segments. Triple that would be 6 arrows every 10 segments—just over 1 arrow every 2 segments. That timing is consistent with the Crossbow of Speed:
In surprise situations it is of no help, but in complete surprise situations the held crossbow will enable its user to fire in the 2nd segment portion.

Gygax himself did not intend that to read as 6 arrows / segment.⁵ Either way, not a flurry of 12+ arrows!

Additional Notes

• A thief Moving Silently can prompt a Surprise roll even when expected.
• A thief failing to Move Silently triggers a Surprise roll for both sides (as the thief doesn’t know they failed their Move Silently).
• An attack when using Dust of Disappearance is always by surprise (assumed for the entire party if silent). Roll normal surprise, with a minimum of 1 segment of surprise for the opponent party.
• A character wearing the Robe of Eyes can easily detect hidden things; surprise of a character wearing a Robe of Eyes due to things being hidden is impossible.
• The Crossbow of Speed can fire during Surprise on the 2nd segment of surprise (“complete surprise”) (DMG, p. 168). Loading and firing a normal crossbow therefore can’t be accomplished during 2 segments of Surprise.
• Sandstorms and frostbite both increase the chance to be surprised by 1 (increasing the party’s potential surprise range by 1) (WSG).
• A garrote attack will only succeed with Surprise from behind.
• While a weapon might be poisoned before the Surprise round, the poison will only affect the first strike: “Blades can likewise be coated with a toxic resin … cause a poison saving throw to be made by the first creature initially struck by such a weapon (PHB, p. 107)”.
• Assassins can don disguise to create the opportunity for surprise (see PHB, p.29).
• Improved Invisibility has the effect of moving considerations for detection of such invisibility downwards by two places compared to other forms of invisibility on the Detection of Invisibility Table, not Surprise, so still increases the range of Surprise by 1 (1-3 in d6) (DMG, p. 47).

Interpretations

• Outdoors, if not surprised themselves, a party with Surprise can withdraw (where possible) unnoticed (DMG, p. 49, 69, 183). Complete Surprise is required (more than 1 segment of surprise) underground.
• Encounter distances are defined for a normal party. But what about the thief (or elves, etc.) moving silently? The “relatively quiet movement” of the lightly-armored thief can only be heard at 30′ (DMG, p. 68). At 30′, roll Surprise (potentially modified by Move Silently), and resolve Surprise encounter distance as normal (d3″) (DMG, p. 62).
• While performing a back stab from Surprise after a successful Move Silently, the thief could be considered to also be invisible (as their opponent can’t see them), surprising on 1-4 in 6 (receiving both the Hidden and Silent modifiers to Surprise).
• The monk’s chance of being surprised drops 2% per level. However, the duration of surprise isn’t necessarily reduced. Reformulating the monk ability, monks are surprised: 2 in d8 at Level 5, 2 in d10 at Level 8, 2 in d12 at Level 10, 2 in d20 at Level 13, and 1 in d20 at Level 16. Invisibility and Stealth modify as normal (e.g., a hidden, silent thief will surprise a Level 5 monk 1-4 in 8).
• If, at the beginning of a round, a new 3rd party has suddenly entered combat, treat this as the beginning of a new encounter. Each engaged party makes a new surprise roll. Surprise is resolved, and then Initiative continues as normal. This is the same explanation as why Surprise for back stab in melee, effectively starting a new encounter (as an encounter is defined as “An unexpected confrontation with a monster, another party, etc.”) (DMG, p. 228). It’s also consistent with when Initiative starts, “when an encounter occurs” (DMG, p. 62). The 3rd party initiates a new encounter, restarting the entire encounter sequence.
• Attacking a (normally) sleeping creature triggers a Surprise check (with a minimum of 1) as if the attacker is Invisible (1-3 in 6).
• Priests of Nerull use the mechanic of “surprised 2 in 12” to represent the ability to be surprised on only 1 in d6, but still be surprised for two segments.¹ Perfect for the Ranger 1 in d6.
• The piercer surprises 95% of the time. Given the piercer’s movement / segment (1′) and inability to attack without falling, the number of segments of surprise aren’t relevant. They either get a free attack, or the party isn’t surprised, and attack order is by Initiative.

Edge Case: Spell casting and Surprise

Two parties roll Surprise. The PCs are surprised for 2 segments. The enemy spell caster begins casting a 3-segment spell. Normally, after two segments both groups would roll Initiative, with the spell caster having 1 segment remaining. But what of the case of a single PC whose Surprise has been modified by encumbrance or a low Dexterity to 3? Of the two possible interpretations:
–The spell caster completes their spell, at a penalty to the party.
OR
–everyone rolls Initiative, and the more-Surprised PC’s additional segment just gets ignored, or integrated in the initiative round.

The latter appears more practical, for this extreme edge case.

Group Surprise Rolls

A ranger is surprised only 1 in d6. If they can convey that to the party, then the party is surprised 1 in d6.

But what if they can’t convey that information? You now have the monsters surprised 2 in d6, the party surprised 2 in d6, and the ranger surprised 1 in d6. In that case the ranger subtracts one from their own individual surprise.

Alertness works similarly, but requiring a proficiency roll when the party surprise is >= 2 segments:
“We are surprised 2 segments”.
“Wait, I have Alertness. *roll*. I’m only surprised for 1 segment.”

The case of three parties in Surprise is the combat example of two parties fighting when a 3rd party comes on the scene. Pause at the beginning of the round, reroll and process Surprise for all 3 groups, and then resume Initiative.

Ambush

The question that often arises is the PCs attempting an ambush. While it’s possible that the PCs can’t be surprised (due to awareness of their opponents), it’s not possible to guarantee surprise for the PCs. Their chance of surprise is 2 in 6. If they’re moderately silent (say more than 90′ away while wearing metal armor), then the GM might grant them “silent”, increasing their chance to 3 in 6. Getting to 4 in 6 would require “hidden”, only possible if the party is thieves, rangers, etc. Magic-users don’t hide so well.

Outdoor encounter range (the point at which the PCs become aware of their opponents) defaults to 6d4″, modified by terrain. Normally, surprise outdoors modifies the encounter range, in addition to the number of segments of free and unanswered activity, subtracting the number of segments of surprise from the encounter range as well.

However, in the case of an ambush, the number of surprise segments should increase the distance between the PCs and their opponents, as surprise provides the PCs more time to prepare, not less.

Example: The PCs, hidden in a grove of trees in a forest, plan to ambush a group of orcs they know will come down the trail, firing at the orcs when the orcs are 12″ away. As the PCs are aware the orcs are coming and can’t be surprised, they don’t roll surprise. The GM rolls surprise for the orcs and rolls a 2 (surprised for 2 segments, and 2 segments further away). The forest will subtract 6″ (1 / die) from the encounter range. The surprise will add 2″.  If the encounter distance (6d4 – 6 + 2)  is now ≥12″, the PCs plans will come to fruition, waiting to fire until the orcs reach 12″. However, if the encounter range is < 12″, the PCs will fire at the encounter range. They’ll get 2 segments to attack, and then both sides will roll for initiative.

It’s important to note that just because the PCs believe the orcs will come down the trail does not guarantee the PCs cannot be surprised, as the orcs could arrive early, have outlying scouts, etc. Rolling surprise for the PCs can still be appropriate.

Wise players won’t argue for the ability to automatically ambush lest the same thing occur to them!

Calculating Cumulative Surprise (Optional)

Any time the range of surprise for a group would be reduced to 0 (e.g. a 0 in d6 chance), the die size is incremented instead (next 1 in d8, then 1 in d10, etc.). Blackmoor uses this for the monk (“At 3rd level monks are surprised only on a roll of 1 in 6, at 5th level only 1 in 8, and at 7th level and above only 1 in 10.”). A party with everyone lightly encumbered with a Dexterity of 17 (a +2 Reaction Adjustment) would therefore be surprised on 1 in 8. If the group also had a ranger, the chance of surprise would be 1 in d10. The same applies to a Surprise chance of 1-6 in d6, instead converting to 1-7 in d8, etc.

For a by-the-book example of a similar methodology, consider the greenhag, which surprises 1-5 in d6. If invisible (which normally would be 1-6 in d6), the greenhag instead surprises 19 in 20.

There are rare instances where surprise could be converted into d100. If the opponent uses a different die than d6 to calculate surprise (d8, d10, even d20), then modifications to their range of being surprised could be calculated on d100 (such as adding 16.67% from the ranger ability to the 5% chance of the creature surprised only 1 in 20). But instead, modify by the same number (applying the “1” from the 1 in 6 chance to the 1 in 20, making the range 2 in 20), because that’s faster, easier, and reflects the increased difficulty to surprise that creature.

Appendix A:  Surprise: An Operational Guide

1. Roll Move Silently (where applicable) and other effects that determine Hidden or Silent (such as Boots or Cloak of Elvenkind) if and only if they apply to the entire party.
   1. Move Silently (and other effects) provide a Base Surprise modifier you need for the next step
2. Determine the potential Base Surprise for each involved Party
   1. Normally 2 in 6, this can be modified by Class, Race/Monster, Stealth/Silence, and Alertness
   2. See https://dnd.sinister.net/im-surprised/ for extended details
3. Roll Base Surprise for each party (normally 1-2 in d6)
4. Determine Encounter Distance
   1. If any party was surprised: d3″ (indoors); 6d4″ modified by terrain – Base Surprise” (outdoors)
   2. If neither party was surprised: d6 +4″ (indoors); 6d4″ (outdoors). Move on to Initiative
   3. Adjust (if necessary) by line-of-sight/ size of room
5. Determine party Surprise duration (in segments)
   1. Surprise duration is the same number that determines if the party was surprised (e.g., a party that rolled a 5 when surprised 1-5 in d6 is surprised for 5 segments)
   2. If neither party is surprised, move on to Initiative
   3. If both parties are equally surprised, move on to Initiative
   4. If only one party is surprised, Surprise duration for that party is the Base Surprise.
   5. If one party is more surprised, Surprise duration (in segments) for the most surprised party is: (most surprised party’s Base Surprise) – (least surprised party’s Base Surprise). Only one party will lose segments and be surprised.
6. Determine individual Surprise duration
   1. Adjust the number of segments each individual in a Surprised party can be affected according to their Dexterity, encumbrance, individual alertness, or other modifiers.
   2. An individual with ≤ 0 Surprise segments remaining will no longer be affected by individual attacks (melee or ranged), but cannot respond in any other way.
7. Process each Base Surprise segment as a full round in but a single segment (actions 4.A-H).
   1. Movement is 1/10th normal (a single segment)
   2. Casting time is by segment. Any spell not completed in a Surprise segment carries over to the next segment of Surprise, and then carries over into Initiative if still not complete.
   3. Ranged weapons fire at three times the normal rate if ready (in other words, if prior to the first surprise segment: “I’ll nock an arrow”, “Ready weapons and missiles”), otherwise at normal rates (e.g., I read this as three arrows the first segment if nocked and ready, and two arrows for later Surprise segments).
   4. Any individual attack (melee or ranged) against a surprised opponent with no remaining individual surprise segments is deferred to Initiative.
8. Process extended Surprise
   1. Any individual with remaining Surprise segments can be individually attacked (melee or ranged) for any remaining individual surprise segment. No other actions by attacker(s) are possible.
9. Roll Initiative
   1. Adjust any spell casting time by whatever arcane method you use for casting time in 1e Initiative.
10. If at any point a new party enters the fray during Initiative rounds, repeat the Surprise process (above).

References

⁴Strategic Review, Vol. 1, No. 2, “Rangers: An Exciting New Dungeons & Dragons Class,” Summer 1975.
Dungeons & Dragons Additional Rules for Fantastic Medieval Wargames Campaigns Playable with Paper and Pencil and Miniature Figures, Supplement 1: Greyhawk. Gary Gygax and Rob Kuntz, 1976.
Dungeons & Dragons Additional Rules for Fantastic Medieval Wargames Campaigns Playable with Paper and Pencil and Miniature Figures, Supplement 2: Blackmoor. Dave Arneson, 1975.
Dungeons & Dragons Additional Rules for Fantastic Medieval Wargames Campaigns Playable with Paper and Pencil and Miniature Figures, Supplement 3: Eldritch Wizardry. Gygax & Blume, 1976.
TSR 2010, Players Handbook, 1978.
TSR 2011, Dungeon Masters Guide, 1979.
Polyhedron #12, “Dispel Confusion”, 1983, p. 10.
Dragon Magazine, Issue 42, “Sage Advice”, October 1980, p. 23.
¹Dragon Magazine, Issue 71, “Deities & Demigods of Greyhawk”, March 1983.
Polyhedron #24, “Dispel Confusion”, 1985, p. 36.
TSR 2017, Unearthed Arcana, 1985.
TSR 2020, Wilderness Survival Guide, 1986.
²Polyhedron #31, “Dispel Confusion”, 1987, p. 29.
⁶Dragon Magazine, Issue 117, “Sage Advice”, January 1986, p. 54.
Dragon Magazine, Issue 133, “Surprise: Determining who gets the drop on whom”, May 1988.
³Zagyg’s Wisdom, https://www.dragonsfoot.org/forums/viewtopic.php?f=50&t=10004&start=180
https://playingattheworld.blogspot.com/2012/08/gygaxs-thief-addition-1974.html [original thief]
http://murphysvictim.blogspot.com/2013/03/1st-edition-ad-surprise-not-so-difficult.html
https://nagorascorner.blogspot.com/2018/05/surprised-and-confused.html [history]
Great Plains Games Players Newsletter #9.
⁴Dragonsfoot.org, March 15, 2005. https://www.dragonsfoot.org/forums/viewtopic.php?f=50&t=10004&p=166208  “As far as my intent went, there was no difference between a blow and a missile attack in regards to surprise. So if there are three segments of surprise, the weapon has a RoF of two per segment, then six attacks could indeed be made thus.”