Eldritch Blast with multiple beams and Agonizing Blast on a single target: Cha Mod just once?

Question

Agonizing Blast allows a Warlock to add Cha mod to EB damage. Two questions:

1. At higher levels, when directing multiple beams at a single target, does it work like Magic Missile, where the modifier is added only once per target (with Empowered Evocation)?
2. Does each beam that hits trigger a concentration check, or, like MM, is considered a single source of damage?

I'm leaning towards "yes" on both because each beam involves a separate attack roll, unlike MM. So, in that sense, it's more like a Warrior's multi-attack than a spell.

Answer 1

Each beam is a separate attack in this case. So

1. Different from Magic Missile. Because each is a separate attack, it's almost like treating it as a separate instance of the spell. It's a separate damage roll to so you add your CHA mod to each instance (magic missile is one damage roll per target).

2. Yes. Again, because they are separate attacks, each beam you target at an opponent, that hits, triggers a new concentration check.

You're exactly right on the comparison, this is a multi-attack spell, rather than multiple damage units like Magic Missile.

Answer 2

1. Yes, each beam gets a bonus.
2. yes each beam is a separate attack and would trigger a concentration check.

Horse's mouth

Answer 3

1. Eldritch blast becomes a multi-attack spell but Agonizing Blast clearly states when you cast EB add your Charisma modifier. You're only casting the spell once so you only get the modifier once. I would assume, at higher levels, when you have the ability to target multiple creatures, you get to choose which one of your eldritch beams becomes "agonizing".

2. Yes.

Here's Agonizing Blast's description for completeness:

When you cast eldritch blast, add your Charisma modifier to the damage it deals on a hit. -- Player's Handbook, page 110