The illusionist's bracers magic item grants the following benefit (GGtR, p. 178):
While wearing the bracers, whenever you cast a cantrip, you can use a bonus action on the same turn to cast that cantrip a second time.
I'm sure everybody sees where this is going. If you don't: eldritch blast.
Since this item is more or less what you want from the Quickened Spell Metamagic, sorcerer can just be thrown in the trash in regards to multiclassing here.
This is all assuming your DM allows this item and you can get your grubby little force-infused paws on them.
But if you know you can get them, this is my recommendation. Everything about this build is legal, though; no UA or outside sources used. Although the sheer ridiculousness of this build doesn't come online until level 20, so keep that in mind.
- Race: Bugbear
- Classes and Levels: 18 Cavalier fighter, 2 Hexblade warlock
- Weapon of Choice: Whip (20-foot reach)
- Fighting Style recommendations: Blind Fighting, Defense, Thrown
Weapon Fighting (for if you get Hasted)
- Invocations: Agonizing Blast, Repelling Blast
- Feats: War Caster, Sentinel, Mobile
War Caster is absolutely essential for this build to function properly. Sentinel and Mobile aren't nearly as necessary but can still help you out.
So, with simply just having eldritch blast and the illusionist's bracers at level 17, you're making 8 attacks every round if you use both your action and bonus action. No additional resource cost, no questions asked. Obviously you can Action Surge as well and get an additional 4 for a total of 12 attacks; nothing new – that seems to be the usual soft cap for attacks per round in 5e.
Where it starts to get crazy is the combination of War Caster and the 10th- and 18th-level features from the Cavalier fighter.
The description of the Cavalier fighter's 10th-level feature, Hold the Line, states (XGtE, p. 30):
[...] Creatures provoke an opportunity attack from you when they move 5 feet or more while within your reach, and if you hit a creature with an opportunity attack, the target's speed is reduced to 0 until the end of the current turn.
And the description of the 18th-level feature, Vigilant Defender, reads (XGtE, p. 30):
[...] In combat, you get a special reaction that you can take once on every creature's turn, except your turn. You can use this special reaction only to make an opportunity attack, and you can't use it on the same turn that you take your normal reaction.
You essentially have an unbound number of opportunity attacks so long as you don't use your reaction, and anything that moves 5 feet within your 20-foot threat radius opens them up to getting blasted 4 times by your eldritch blasts. If any of them hit, that creature's movement is reduced to 0. If you grabbed Sentinel, they can't even use the Disengage action at that point; you'll still get to attack them. And if you got Blind Fighting, invisibility and darkness won't help them either if they get within 10 feet of you.
You are a biological Gatling gun.
So, you have 8-12 attacks a turn, split up however you like. Then 4 more eldritch blasts on a single creature every time it even looks in your general direction.
So you'll also be winning most magical quick-draw competitions as well.
If your party members want to help with this insanity, they could cast enlarge on you to increase your threat range even further, thereby netting you more theoretical attacks.
The raw DPR of this build isn't too shabby either, especially if you can get Hexblade's Curse and hex off.
It's very likely my math is wrong, but I think it came out to something like 252 average force damage if all 12 blasts hit with both hex and the Curse active.
Either way, that's my 2 cents. Have fun playing Bugbear Belmont; you can flavor the eldritch blasts as your flaming whip :)
Just be careful if you come across a Tarrasque. Maybe let your other, slower party members handle that.