The Evocation Wizard's 14th level ability Overchannel says (in part):
When you cast a wizard spell of 5th level or lower that deals
damage, you can deal maximum damage with that spell.
Bigby's Hand is a 5th level Evocation that lasts up to 1 minute with concentration. During this duration, the caster can cause one of several effects on each of her turns. Some of them cause damage, and some of them do not. The two that can cause damage are:
Clenched Fist. The hand strikes one creature or object within 5 feet of it. Make a melee spell attack for the hand using your game
statistics. On a hit, the target takes 4d8 force damage.Grasping Hand. The hand attempts to grapple a huge or smaller creature within 5 feet of it. […] While the hand is grappling the
target, you can use a bonus action to ahve the hand crush it. When
you do so, the target takes bludgeoning damage equal to 2d6 + your
spellcasting ability.
If the caster overchannels this spell, do these effects both do maximum damage on any turn on which the caster chooses one of them?
Best Answer
Yes, that is what the text is saying. Bigby's hand is a spell and can deal damage. If it does deal damage, and you've overchanneled, it deals maximum damage. The number of separate rolls involved and the time between casting and damage and all the other things like that are completely irrelevant to the rules in both descriptions.
The only reason this seems unclear, as far as I can tell, is because overchanneling seems more better for this spell than others, so people are hesitant to let it apply. In actuality, overchannel nearly always simply doubles the expected random damage of a spell; it's just that this spell is capable of a lot of total damage so the absolute expected gain is larger.
Other benefits of overchanneling, like a deviation of 0, apply equally to this and other spells.