Thorough Investigation — ruling 1

Thorough Investigation's first ability can trigger only once per combat, no matter how many creatures you attack with.

Thorough Investigation — ruling 2

To venture into the dungeon, a player moves their venture marker into the next room of the dungeon they are currently in. If they aren't currently in a dungeon, that player instead chooses a dungeon card from outside the game, puts it into the command zone, and moves their venture marker onto the first room.

Thorough Investigation — ruling 3

Moving into a dungeon room will cause its room ability to trigger.

Thorough Investigation — ruling 4

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

Thorough Investigation — ruling 5

A player may only have one dungeon in the command zone at a time.

Thorough Investigation — ruling 6

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.

Thorough Investigation — ruling 7

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.

Thorough Investigation — ruling 8

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

Thorough Investigation : règles, fonctionnement et interactions (MTG)

Thorough Investigation is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever you attack, investigate. (Create a Clue token. It's an artifact with ", Sacrifice this token: Draw a card.") Whenever you sacrifice a Clue, venture into the dungeon. (Enter the first room or advance to the next room.)

How it works : Thorough Investigation

Original English text — Wizards of the Coast / Scryfall

#1July 23, 2021· Wizards of the Coast
Thorough Investigation's first ability can trigger only once per combat, no matter how many creatures you attack with.
No other card is named in this ruling.
#2July 23, 2021· Wizards of the Coast
To venture into the dungeon, a player moves their venture marker into the next room of the dungeon they are currently in. If they aren't currently in a dungeon, that player instead chooses a dungeon card from outside the game, puts it into the command zone, and moves their venture marker onto the first room.
No other card is named in this ruling.
#3July 23, 2021· Wizards of the Coast
Moving into a dungeon room will cause its room ability to trigger.
No other card is named in this ruling.
#4July 23, 2021· Wizards of the Coast
Once you resolve the last room ability of a dungeon, that dungeon is now completed and is removed from the game.
No other card is named in this ruling.
#5July 23, 2021· Wizards of the Coast
A player may only have one dungeon in the command zone at a time.
No other card is named in this ruling.
#6July 23, 2021· Wizards of the Coast
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.
No other card is named in this ruling.
#7July 23, 2021· Wizards of the Coast
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.
No other card is named in this ruling.
#8July 23, 2021· Wizards of the Coast
You can only move forward (well, downward) in a dungeon, never backwards or sideways.
No other card is named in this ruling.
#9July 23, 2021· Wizards of the Coast
Dungeons are removed from the game as a state-based action.
No other card is named in this ruling.
#10July 23, 2021· Wizards of the Coast
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.
No other card is named in this ruling.
#11July 23, 2021· Wizards of the Coast
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.
No other card is named in this ruling.