Last Revised: 221102
From previous analysis, the elf ability to Surprise on 1-4 in d6 when not in metal armor and 90′ in advance derives from +1 from being hidden, and +1 from being silent. That’s consistent with the PHB example—a party moving silently and invisibly is +2 to their chance to Surprise.
But does the elf adjustment derive in any way from being hidden? From the PHB: “If alone and not in metal armor … an elven character moves so silently that he or she will surprise monsters [1-4 in 6].” There’s no mention of being hard to see. From the MM entry for the elf: “When in natural surroundings such as a wood or meadow, elves can move silently (surprise on a 1-4) and blend into the vegetation so as to be invisible (requiring the ability to see invisible objects to locate them) as long as they are not attacking.” Again, their (improved) ability to Surprise is attributed only to silence. Both the elf and halfling also lose their +2 to surprise if they have to open a door, where the noise from a door is attributed to a noisy failed attempt (DMG, p. 62).
Silent + invisible improves surprise to 1-4 in d6. The thief “Move silently” is only “little sound and disturbance”, not “completely silent”. Could the elf be, well, extra silent? Bugbears (“silent creatures”, “with great stealth”, “will never be heard”) only add +1. Yet there’s support for “extra silent” enhancing Surprise. The giant owl flies “with nearly absolute silence, thus it surprises on 1-5 (on a 6-sided die).” Unicorns “move very silently and surprise opponents on a 1-5.”
There are other creatures that surprise on 1-5 with improved hiding: The huge spider, attributed to some combination of carefully hidden places and leaping; the xorn blending into stone; the giant lynx “hide themselves”. The invisible stalker surprises on 1-5 in 6, which isn’t attributed to anything (although clearly “invisible” is part of it).
Clearly it’s possible to improve the chance to surprise by being extra hidden or extra silent. Potentially blending into the background of the world so well as to be more hidden than invisible, and more silent than total silence. In a way that makes sense—an absence of noise at all is, in and of itself, noticeable. An invisible character still leaves traces in the dust on the floor and air.
But is the elf specifically not hidden? Digging deeper, UA ascribes the elven ability to hiding: “[Solonor] taught the first elves the art of hiding in and moving through natural foliage so as not to be detected” suggests attributing some elven ability hiding. Looking at the MM halfing: “exceedingly clever at both quiet movement and hiding … surprise on a die roll of 1-4 on a 6-sided die. In natural terrain they must be treated as invisible if they have any form of vegetation in which to conceal themselves.” Very similar to the elf description(s), except that the quiet movement and hiding are both attributed to their ability to surprise. The elven surprise ability can be assumed the same as the halfling, since they can travel together and maintain their enhancement. So either the elf ability is silent + hidden, or the halfing is also extra silent.
From the above, if the elven surprise ability does not include hiding, they’re:
+1 to Surprise because they’re silent
+1 to Surprise because they’re an elf (and extra silent)
which means an additional +1 if they’re somehow hidden as well—a significant increase in the elf’s ability to surprise. If invisible, or in natural surroundings, the elf would surprise 1-5 in 6, surprising 61% of the time, 42% of the time for 3 or more segments.
So does the elven ability not include being hidden? Elves have almost the same enhancement to Hide in Shadows (+10%, +15% for halflings). Assuming the elven ability derives only from silence ignores indirect references to their being hard to see. However, to my mind most significant is that both halfling and elven abilities include the ability to be “hidden”/”as to be invisible”/”hiding”. If they are “extra silent” their surprise ability would more accurately be presented as 1-5 in 6, and it’s not. I’m sticking with +1 hidden, +1 silent. It’s an interesting approach however, significantly modifying Surprise in the party’s favor.