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> Nat 20
> The spell fails anyway because (a) congenital disabilities aren't wounds and (b) crits only apply to attacks to begin with
I've seen many a game have a "absolute success/failure" rule.
Makes for good stories usually.
Also no healing spell requires an attack roll. In 3rd edition there were some spells that were Save (Harmless) that you could choose to try to make a saving throw to resist them. Once I was playing an Athar who would resist any spell granted by a deity but it was me rolling the dice not the caster.
Cast Animate Object on the wheelchair and make it spin in place as fast as possible for the entire spell duration. Weeeee!