Sefris of the Hidden Ways — ruling 1

Sefris of the Hidden Ways must be on the battlefield for its first ability to trigger. It does not trigger when Sefris goes to the graveyard from the battlefield, even if other creature cards also went to the graveyard at the same time.

Sefris of the Hidden Ways — 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.

Sefris of the Hidden Ways — ruling 3

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

Sefris of the Hidden Ways — ruling 4

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

Sefris of the Hidden Ways — ruling 5

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

Sefris of the Hidden Ways — 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.

Sefris of the Hidden Ways — ruling 7

Sefris of the Hidden Ways' first ability looks only at the type the card has in the graveyard, not the type it had in any other zone. For example, animated lands dying won't cause the ability to trigger. The opposite is also true. For example, if a creature that was cast as an Adventure is countered, it's a creature card in the graveyard and the first ability will trigger.

Sefris of the Hidden Ways — ruling 8

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

Sefris of the Hidden Ways : règles, fonctionnement et interactions (MTG)

Sefris of the Hidden Ways 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 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.

How it works : Sefris of the Hidden Ways

Original English text — Wizards of the Coast / Scryfall

#1September 24, 2021· Wizards of the Coast
Sefris of the Hidden Ways must be on the battlefield for its first ability to trigger. It does not trigger when Sefris goes to the graveyard from the battlefield, even if other creature cards also went to the graveyard at the same time.
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
Sefris of the Hidden Ways' first ability looks only at the type the card has in the graveyard, not the type it had in any other zone. For example, animated lands dying won't cause the ability to trigger. The opposite is also true. For example, if a creature that was cast as an Adventure is countered, it's a creature card in the graveyard and the first ability will trigger.
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.
#12July 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.