Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice
Mardu Siegebreaker.
Mardu Siegebreaker leaves the battlefield, causing
Tomb of Horrors Adventurer to be returned to the battlefield from exile.
When
Tomb of Horrors Adventurer enters, it and
Radiant Solar trigger.
Resolve the
Tomb of Horrors Adventurer trigger, venturing into the Cradle of the Death God room, creating a 4/4 legendary The Atropal creature token and completing
Tomb of Annihilation.
If you control two or more The Atropal tokens, put all but one into your graveyard due to the legend rule.
Sefris' second ability triggers, returning
Mardu Siegebreaker from your graveyard to the battlefield.
When
Mardu Siegebreaker enters, it and
Radiant Solar trigger.
Resolve the
Mardu Siegebreaker trigger, exiling
Tomb of Horrors Adventurer until
Mardu Siegebreaker leaves the battlefield.
Resolve the
Radiant Solar trigger from step 10, venturing into
Tomb of Annihilation and into the Trapped Entry room, causing each player to lose 1 life.
Resolve the
Radiant Solar trigger from step 6, venturing into the Oubliette room, causing you to discard a card and then sacrifice
Mardu Siegebreaker.
Repeat from step 5.
Results
Near-infinite ETB.
Near-infinite death triggers.
Near-infinite lifeloss for all players.
Near-infinite sacrifice triggers.
Near-infinite LTB.
Metadata
In 9 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Exhibition (Bracket 1+).