Grim Hollow Feat "Lightning Caster"

So it goes as so. 

Technically, if you target all the beams at 1 creature, you can target a second creature once as a Bonus Action. You are getting an additional target, not an additional casting of the spell.

I agree. It's technically legit, and the second creature would receive only one beam.

I think we can find an equivalent interaction with War Caster + Eldritch Blast. I shared this in a thread about the War Caster feat:

Quote from Tarod_ >>

While not official ruling, this is from the Dev:

@thomas_conners Can warcaster be used to cast a lvl 5+ Eldritch Blast as long as all the rays target only the provoking creature?
@JeremyECrawford Yes

I admit I agree with that.

Like a lot of homebrew stuff, this is badly written and open to many possible interpretations. 
It doesn't say if you make another attack roll, it doesn't say if saving throw cantrips work, it doesn't say if you roll the damage once or twice, and it doesn't give any indication on how to handle the special case of Eldritch Blast.
So... anything goes, really. It's between you and the DM :)

If I was the DM in this case, I would say that it doesn't work at all. I would interpret "a cantrip with a casting time of an action that targets a single creature" as a cantrip that can only target a single creature. If it's an attack roll, make another attack and damage rolls, and if it's a saving throw, roll 2 instances of damage.
Eldritch Blast is busted enough as it is :)

Quote from Natrel >>

Like a lot of homebrew stuff, this is badly written and open to many possible interpretations. 

It's third party, a step up from homebrew. As with all third-party content, the quality varies. I believe this publisher has a reputation for being one of the better ones though.

Quote from Natrel >>

It doesn't say if you make another attack roll, it doesn't say if saving throw cantrips work, it doesn't say if you roll the damage once or twice, and it doesn't give any indication on how to handle the special case of Eldritch Blast.

I think all of that is pretty obvious. Essentially, it's expending a Bonus Action while you cast the spell to increase the targets, similar to the 2024 Twinned Spell metamagic. Unlike Twinned Spell, it applies to Cantrips and just gives you an extra target. At level 17, you can Firebolt two targets for 4d10 damage for a Magic Action and a Bonus Action.

Now, if someone triggers an Attack of Opportunity on your turn and you use your reaction to cast a cantrip at that creature, can you still use this to target a second creature?

Quote from Rationale01 >>

So it goes as so. 

Ability Score Increase. Increase your Int, Wis, or Cha score by 1, to a max of 20.

Dual Target. When you cast a cantrip with a casting time of an action that targets a single creature, you can use a Bonus Action to target a second creature within the cantrip's range.

Immediate Response. Once per Long Rest, when you cast a spell as a Reaction, that spell doesn't expend a spell slot.

Simple question here. I'm using Eldritch Blast at 11th level. 3 blasts per casting. Does this mean:

I must target all 3 beams at 1 creature, and then hit another creature with 3 beams ( I must roll 6 times)

or

I can target three creatures ( a single creature per blast), and therefore target 3 other creatures within range.'

or

Some other interpretation.

What say you DnD community. My DM and I have already discussed. But would like to see how other DM's rule on this. 

 

 

The established interpretation from the 2014 Twinned spell days, which is what this feat seems to be echoing, is that it would need to be a spell that doesn't even give you the option of targeting multiple creatures

Under that interpretation, EB wouldn't be eligible for the feat at all