Radiant Solar + Sefris of the Hidden Ways + Barrowin of Clan Undurr + Mardu Siegebreaker

Radiant Solar

Sefris of the Hidden Ways

Barrowin of Clan Undurr

Mardu Siegebreaker

How it works

1. Cast Mardu Siegebreaker by paying its mana cost.
2. When Mardu Siegebreaker enters, it and Radiant Solar trigger.
3. Resolve the Mardu Siegebreaker trigger, exiling Barrowin of Clan Undurr until Mardu Siegebreaker leaves the battlefield.
4. Resolve the Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Mardu Siegebreaker.
5. Mardu Siegebreaker leaves the battlefield, causing Barrowin of Clan Undurr to be returned to the battlefield from exile.
6. When Barrowin of Clan Undurr enters, it and Radiant Solar trigger.
7. Resolve the Barrowin of Clan Undurr trigger, venturing into the Cradle of the Death God room, creating a 4/4 legendary The Atropal creature token and completing Tomb of Annihilation.
8. If you control two or more The Atropal tokens, put all but one into your graveyard due to the legend rule.
9. Sefris' second ability triggers, returning Mardu Siegebreaker from your graveyard to the battlefield.
10. When Mardu Siegebreaker enters, it and Radiant Solar trigger.
11. Resolve the Mardu Siegebreaker trigger, exiling Barrowin of Clan Undurr until Mardu Siegebreaker leaves the battlefield.
12. 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.
13. Resolve the Radiant Solar trigger from step 6, venturing into the Oubliette room, causing you to discard a card and then sacrifice Mardu Siegebreaker.
14. Repeat from step 5.

This loop transforms Sefris of the Hidden Ways into an engine of endless dungeon crawls by continuously cycling creatures through the graveyard and battlefield. Mardu Siegebreaker acts as the blink engine, exiling Barrowin of Clan Undurr upon entry until it is sacrificed, which simultaneously triggers Sefris's graveyard-to-battlefield return mechanism whenever legend rules or dungeon completions send pieces away. Meanwhile, Radiant Solar provides the critical mass of dungeon ventures upon every single entry, and Barrowin of Clan Undurr accelerates the cycle by entering the battlefield to push you deeper into the dungeon until you complete Tomb of Annihilation repeatedly.