Going by Warcraft interpretation - Warlocks specializes in infernal-magicks and invocations, summoning demons to fight enemies as minions and throwing hexes, curses and otherwise dark eldritch powers around to cause major damage. They often either draw their powers through their innate darkened soul or through pacts with eldritch horrors and demons.
Oh, yes. Even better, she has the slave Daemons she liberated (from our RP on the "Twilight to Battle" art) as backup!
Cue attempted "Not So Different" speech by Warlock-Twilight...which Slayer-Twilight cuts off with her own speech about how SHE didn't need to summon her "minions" with magic, but they serve her willingly.