A campaign with a dedication to the spell, Fly, can be very different. PCs who Fly add literally a 3rd dimension to the game. That dynamic extends beyond basic movement considerations to the specifics of casting spells while flying. So what restrictions are on spellcasting while flying? When not flying? In short (for those who don’t care about the why):
- Spellcasters cannot cast spells unless stationary for the entire round. Exception: Flying characters can cast spells when moving slowly (<3″)
- Spellcasters cannot cast spells when carrying someone (flying or otherwise)
- Spellcasters cannot cast spells when being carried (flying or otherwise)
In short, spellcasters cannot cast spells when limited or restricted physically.
Spellcasters cannot cast spells when carrying someone, as casting is not possible when hindered:
- PHB, p. 100: “Physical restraint, including grappling, grasping, binding, etc. prevents proper somatic spell completion, for gestures must be exact and movements free and as prescribed.”
- DMG: “The somatic portion of a spell must be begun and completed without interruption in a clean, smooth motion. Spells cannot be cast while violently moving – such as running, dodging a blow, or even walking normally … Thus casting a spell requires that the figure be relatively motionless and concentrating on the effort during the entire course of uninterrupted casting … the caster cannot be crouching, let along prone, during casting. … a mere shove at any time can spoil the dweomer.”
Further insight comes from spellcasters’ inability to cast spells while walking, even through they CAN marginally cast spells while flying (“most spells can be cast when Flying while hovering or moving slowly (defined as 3”)). If the PC must be standing, and when not flying can’t be moving, then the whole body must be involved in the somatic casting process. Flying must mean the PC can move (slowly) but still gesture with your legs, since the legs are not involved in locomotion.
PCs can’t cast spells when riding a flying mount, or when on a Broom of Flying. Even a magic carpet, “the most stable of flying devices,” only permits casting when “hovering or moving slowly,” and a magic carpet is significantly more stable than being carried by someone else.
That begs the question of when is casting not possible in general for a normal caster? If a character has a backpack of gear? Certainly possible. If they have a backpack full of halfling? The right answer is to integrate encumbrance (which includes “bulkiness”) into the consideration of “hindering.” Encumbrance can be broken into (two different ways, great editing TSR):
- None: Nothing of real import.
- Normal (Light): carrying 35# of gear with no great bulk.
- Heavy (Moderate): Armor and equipment up to about 70# or fairly bulky.
- Very Heavy(Heavy): Armor and equipment of 105# and/or bulky
Encumbered (Severe): up to 150# and/or very bulky.
Extrapolating from encumbrance, given that some the multi-class PCs (Fighter/Magic-user) can cast spells in plate armor with backpack (45# + 40#), casting has to be possible into Very Heavy/Heavy category. Casting would only be restricted in the “Encumbered/Severe” category (which includes almost all cases of carrying someone), as the PC is too encumbered to be able to cast spells in a “clean, smooth motion.”
In the context of the Fly spell, I define lifting limits of Fly to that which a character can carry (150# from Appendix O, modified by Strength). Since a halfling weighing 60 lbs. can carry the same amount as a Barbarian weighing 300 lbs, average Strength (not size) is pegged to being able to lift 150#. While a character with an 18/00 Strength would be able to lift/carry 450# when flying, they still would be unable to cast spells (because of the limitations defining freedom of movement).
For the most extreme of cases, the character with an 18/00 Strength would (in most cases) be able to carry another PC, but that carried PC cannot cast spells while being carried.
There’s a reason why physical limitations on spellcasting are important. In a world where spellcasters could cast spells with few physical restrictions, they become high-risk captives; the best solution would be to kill them off and be done with it. Even if they couldn’t cast spells when gagged, the risks would be too great. If tying them up (or restricting their movement) prevents them from casting spells, holding them as captives becomes a viable alternative.