Nadaar, Selfless Paladin

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

Choosing the dungeon or room to venture into is part of resolving the venture into the dungeon keyword action. Once that choice is made, players may not respond until after the appropriate room ability has triggered.

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.

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.

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.

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

Nadaar doesn't need to have been on the battlefield when you completed a dungeon for its last ability to function.