Sefris of the Hidden Ways

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.

Secret Lair Drop

Forgotten Realms Commander

Forgotten Realms Commander Display Commanders

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