Displacer Beast

You can only move forward (well, downward) in a dungeon, never backwards or sideways.

Dungeons are removed from the game as a state-based action.

Once you resolve the last room ability of a dungeon, that dungeon is now completed and is removed from the game.

Dungeon cards are not part of a player's deck or sideboard. In both constructed and limited formats, players can use any dungeon card when they venture into the dungeon.

The player venturing into the dungeon chooses which dungeon they will venture into. They may choose a dungeon that they have already completed this game.

If you somehow venture into the dungeon while a room's ability is on the stack, you will continue on in the dungeon. If you're already in the last room, complete that dungeon and start a new one.