Hawk Diesel
Adventurer
At the moment it feels like an invocation tax, but that's partly because of how valuable the beams*modifier damage is.
Right. Which is why rather than have it be an invocation, it is rather an upgrade that all warlocks will have access to upon reaching a given level. This also ensures that anyone that dips Warlock cannot wait until they can access invocations and grab this. Will help make more investment needed for the Agonizing Blast effect, but without requiring the expenditure of an Invocation.
Equally unsure. Changing energy type seems good, but if the base is force I can't see that they'd need it. Therefore the base must not be force.
I see what you are saying, and I don't necessarily disagree. But I think the fact that Eldritch Blast deals force damage is really part of the charm of the ability. At the same time, it is also a blessing an a curse. While nothing is really resistant to force damage, nothing is also vulnerable to it. Logistically and mechanically, force damage is not very different from Bludgeoning / Slashing / Piercing damage made with a magic weapon. 90% of creatures that are resistant to Bludgeoning / Slashing / Piercing have that resistance overcome once that damage comes from a magical source. And many class abilities put that ability to deal magical weapon damage (such as the Monk or Moon Druid) at around level 5. This means having force damage is equivalent to at most a level 5 ability. But once again, it will never benefit from vulnerabilities that a creature might have. Allowing to work in a way for that to happen can be nice. It doesn't even need to be a feature, but rather an opt-in ability through an invocation.
I don't think there is a great reason for eliminating other cantrips though... I suppose you are saying make Blast more interesting so that variety in play is achieved with it alone. That might be hard... or even unnecessary given the variety in damage-dealing cantrips that already exists.
I'm not saying eliminating cantrips from the Warlock. Just the offensive ones. Eldritch Blast becomes an offensive Swiss Army Knife of sorts, but still give them access to the defensive or utility cantrips.
Applying multiple at once is already part of a Warlock, e.g. they can apply Repelling and Lethargy to the same cast of EB. You could be right about the Once per turn on your own turns thing. That could be an unnecessary debuff.
In case it is helpful, here is the way I rule it. Agonizing Blast applies to every ray from Eldritch Blast. Period. This is no different than someone using a longbow, except they average 1 more point of damage per attack/ray. I see nothing wrong with this.
Other things like Repelling Blast and Lethargy also apply to every ray. However, an enemy can be affected no more than once per turn. So if you have two shots with a Repelling Blast and you use both to hit one guy, he will only get knocked back 10 feet. But if you use those two blasts to hit two different guys, they each get knocked back 10 feet. From my perspective, to allow any more would be a ridiculous amount of battlefield control for one character.