Secret Lair Countdown

Artifact

Whenever another permanent you control enters, each opponent mills a card.

Altar of the Brood

Secret Lair Drop

Undercity // The Initiative

Seasoned Dungeoneer

Creature — Human Warrior

When this creature enters, you take the initiative.
Whenever you attack, target attacking Cleric, Rogue, Warrior, or Wizard gains protection from creatures until end of turn. It explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on the creature, then put the card back or put it into your graveyard.)

Creature — Cat Beast

Avoidance — Whenever you cast a noncreature spell, exile up to one target nonland permanent you control, then return that card to the battlefield under its owner's control.

Displacer Kitten

Enchantment

{B}, Discard a creature card: Return target creature card from your graveyard to your hand.

Tortured Existence

Dungeon of the Mad Mage

Lost Mine of Phandelver

Tomb of Annihilation

Legendary Creature — Human Wizard

Whenever one or more creature cards are put into your graveyard from anywhere, venture into the dungeon. This ability triggers only once each turn. (To venture into the dungeon, enter the first room or advance to the next room.)
Create Undead — Whenever you complete a dungeon, return target creature card from your graveyard to the battlefield.

Sefris of the Hidden Ways

Legendary Enchantment — Background

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