How does resistance or immunity to psychic affect the Feeblemind spell? Obviously, it would lower the damage they'd take, but does it change the other aspects of the spell?
Resistance would not provide any other benefit against Feeblemind. Resistance is defined as:
If a creature or an object has resistance to a damage type, damage of that type is halved against it. (PHB, 197)
That's it. They would take half damage from the initial spell cast, but all other effects would still apply to them.
As for if a creature has immunity to Psychic, there is a relevant tweet from Mr. Crawford:
Vicious mockery: the second effect isn't reliant on the psychic damage getting through. (Jeremy Crawford tweet).
While Vicious Mockery and Feeblemind are obviously wildly different spells, the result is still the same. Even if something is immune to the damage of a spell, the other effects still apply.
This is also backed up by the Monster Manual:
Some creatures have vulnerability, resistance, or immunity to certain types of damage. Additionally, some creatures are immune to certain conditions. If a monster is immune to a game effect that isn't considered damage or a condition, it has a special trait. (MM, 8).
Immunity to damage, immunity to conditions, and immunity to "game effects" are all different traits. Something being immune to Psychic damage does not mean they are immune to the conditions or effects of that spell unless otherwise stated. As a result, a creature immune to psychic damage would only be immune to the damage portion of Feeblemind, and all other effects would still apply.
This would, of course, also be up to the DM. They may rule that "Psychic immunity" covers all things to do with Psychic spells, or that they have advantage on the Int saving throw required for Feeblemind.
protected by doppelgreener♦ Feb 19 at 12:43
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