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.

When Barrowin enters, venture into the dungeon. (Enter the first room or advance to the next room.) Whenever Barrowin attacks, return up to one creature card with mana value 3 or less from your graveyard to the battlefield if you've completed a dungeon.

Room abilities of dungeons you own trigger an additional time.

Creatures you control can't be blocked except by legendary creatures. Whenever one or more creatures you control deal combat damage to a player, venture into the dungeon. (Enter the first room or advance to the next room.)

Flying, lifelink Whenever this creature or another nontoken creature you control enters, venture into the dungeon. (Enter the first room or advance to the next room.) {W}, Discard this card: Venture into the dungeon and you gain 3 life.

At the beginning of your upkeep, each opponent loses X life and you scry X, where X is the number of Zombies you control. {2}{U}{B}: Exile target creature card from a graveyard. Create a token that's a copy of it, except it's a 4/4 black Zombie. When The Scarab God dies, return it to its owner's hand at the beginning of the next end step.

Commander creatures you own have "Room abilities of dungeons you own trigger an additional time."

Counter target creature or planeswalker spell. Venture into the dungeon. (Enter the first room or advance to the next room.)