Many spells where you can select targets specify you must select targets that you can see, for example Seeming:
This spell allows you to change the Appearance of any number of creatures that you can see within range.
However there are some spells which don't require seeing. I am considering the Paladin spell Destructive Wave for a character of mine (for its ability to knock targets prone), and it has this text:
You strike the ground, creating a burst of divine energy that ripples outward from you. Each creature you choose within 30 feet of you must succeed on a Constitution saving throw or take [damage and be knocked prone, save for half damage]
I would think this clearly allows using this spell even when blind, or against invisible creatures, if the target is not hidden. Also, line-of-effect rule is also in effect, because why wouldn't it be, right? (This is not the question, just assumptions I am making, and I'm pretty sure the DM will also make.)
But is it allowed to choose creatures which are also hidden from the caster, when the spell doesn't require caster seeing the targets?
There are at least these cases to consider:
- Creatures which the caster knows about, but which are hidden, so their location is uncertain to the caster. They may or may not be within range, but the caster wants them to be affected if they are.
- Hidden creatures, which the caster doesn't even know about, but the caster wants to choose every creature within 30'.
- Creatures the caster knows, but has no reason to think they might be within the spell range.