Targeting a huge but "hidden" target with a spell

[Ancalagon]

Hello

I have a fight coming up (as a DM) with a very large creature with strong offensive capabilities (both melee and ranged) but who is immobile.

I was thinking... the smart thing to do for the party is to create a visual screen (a smoke bomb for example) , then fire through the screen at the huge monster. They don't need to aim precisely because they know exactly where the target is, and even if they are off by 5 feet they are still hitting the monster. Meanwhile the monster has a hard time retaliating because it can't see exactly where the PCs are.

Now for arrows etc, this is pretty straightforward, and I might give the heroes a small penalties to hit but no more than that. Where I'm a bit... unsure as to how the rules work, is with spells.

Area of effect? Easy. Just chuck a fireball etc. But what about a spell that targets a foe? Like eldritch blast? Or magic missile? Or hold person?

Thanks!

 

[iserith]

A lot of spells require that the caster see the target. If they can't see it, then they can't target it with the spell.

 

[Ancalagon]

A lot of spells require that the caster see the target. If they can't see it, then they can't target it with the spell.

You're right! Each spell specifies if a visual line of sight is required or not! It turns out that there is no general rule because it's already specified. Well that was easy, thanks!

 

[Cap'n Kobold]

Hello

I have a fight coming up (as a DM) with a very large creature with strong offensive capabilities (both melee and ranged) but who is immobile.

I was thinking... the smart thing to do for the party is to create a visual screen (a smoke bomb for example) , then fire through the screen at the huge monster. They don't need to aim precisely because they know exactly where the target is, and even if they are off by 5 feet they are still hitting the monster. Meanwhile the monster has a hard time retaliating because it can't see exactly where the PCs are.

Now for arrows etc, this is pretty straightforward, and I might give the heroes a small penalties to hit but no more than that. Where I'm a bit... unsure as to how the rules work, is with spells.

Area of effect? Easy. Just chuck a fireball etc. But what about a spell that targets a foe? Like eldritch blast? Or magic missile? Or hold person?

Thanks!

Note that (other factors being normal) anything that requires a roll to hit will be at disadvantage if firing blind, whether spell or arrow, even if they are automatically being targeted at a space that the monster occupies. "Making contact with some part of a target" is only part of what an attack roll vs AC represents.

 

[mellored]

Now for arrows etc, this is pretty straightforward, and I might give the heroes a small penalties to hit but no more than that. Where I'm a bit... unsure as to how the rules work, is with spells.

Just FYI, per the rules, the target not being able to see the attacker gives them advantage, and the attacker not being able to see the target gives disavantage.
So blocking sight both ways means each shot will be normal, both ways.

And IMO, an immobile target would have low (5-10) AC. Though could have a lot of HP.

Though, do whatever's fun for your group.