When Acererak enters, if you haven't completed Tomb of Annihilation, return Acererak to its owner's hand and venture into the dungeon.
Whenever Acererak attacks, for each opponent, you create a 2/2 black Zombie creature token unless that player sacrifices a creature of their choice.
Cast Acererak cheap and grind value: he venturing on every recast and his attack trigger forces each opponent to either sacrifice a creature or hand you a 2/2 Zombie — both great outcomes for a mono-black aristocrats/tokens deck. The real engine is making him cost 0 with reducers so you can loop cast/venture (entering a dungeon other than Tomb of Annihilation so he keeps bouncing) for arbitrary spell-cast triggers, then close with Aetherflux Reservoir. Outside the combo you go wide with Zombies and drain the table with sacrifice payoffs.
Self-bouncing ETB makes him cheap, near-impossible to keep dead, and immune to most removal value loss
Attack trigger punishes opponents either way — board presence or forced sacrifices
Hard combo finish with cost reduction + Aetherflux Reservoir using infinite cast triggers
Strong synergy with venture/dungeon payoffs and the full mono-black aristocrats package
Mono-black gives access to the best tutors and recursion to assemble pieces
Combo relies on stacking multiple cost reducers, which are slow and fragile to artifact/enchantment removal
Mono-black struggles with flying defense and resolved noncreature permanents
Attack trigger only matters if you can profitably attack and have sac payoffs online