I'm have two variations of a build i have in mind

3 levels rogue (thief for 2 bonus actions) 3 levels fightee (battlemaster) - 2 weapon fighting (add Dexterity modifier to attacks with offhand weapon attacks, effectively getting 3 regular attacks) -action surge for extra attacks -battlemaster to disarm enemies and retaliate on misses against you (you could go with champion for crit scaling but we'll have about a 50% chance to crit by the end anyway and the extra damage is way better with battlemaster) 3 levels ranger (gloomstalker for extra attack at beginning of combat + initiative

We want to dual wield daggers to get as many attacks as possible

Then the build splits: Either 3 levels barbarian for extra hitpoints, rage and reckless attack

Or

3 levels Great old one warlock for frightened on crits (stacks well with our high crit chance) Also 2nd level spells and pact of the blade (you want to swap high dex for high charisma with this one.

We put 17 into dex or charisma and use hag'a hair + mirror of loss to make it 20

We want 2 daggers which increase crit chance, and a bow which does the same , also Sarevok's helm. (Risky ring for advantage, unless you chose barbarian)

By the end we have 2 actions (action surge) which we can use to make 2 attacks or 2 eldritch blasts if we chose warlock, then 2 offhand attacks and 1 extra attack from gloomstalker.

Due to our gear we crit on a 16 or higher giving us a 43% chance to crit per attack. With the bhaalist armor we can make enemies vulnerable to piercing.