Since the possibility of having multiple darkness subclasses is being talked of, why not refine the artifact that allowed converting a minion to fight for you in D1? Make it the melee charge for all three classes within the subclass and you can have as many red bar enemies taken as long as you can keep them alive and with every charge of your melee?
It would perhaps give us a reason to go back to the dreadnaught in Witch Queen, perhaps find a source of taken power within it with Savathun making her quick approach. Fight fire with fire. Taken with Taken.
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Alternatively, have the artifact change the effect of your melee charge to give a guaranteed take over at the cost of your charges melee and have it so only a certain number of enemies can be controlled at a time. You could control any enemy except bosses and the number controlled can be upgraded. The limitations would be that ONLY the max number can be controlled (we’ll call these notches), and that the better the minion (I.e. red, orange, yellow health) the more of your “notches” it takes up. Ideally, this means the player can control up to: 2 yellows, 3 orange, or six red at a time. Minions deal extra damage and only disappear either when the player wipes, completes mission, or when they’re killed. otherwise they follow the player and teleport to them whenever they get far or can’t be reached.