Sefris of the Hidden Ways + Radiant Solar + Phantasmal Image + Mercurial Pretender

Sefris of the Hidden Ways

Radiant Solar

Phantasmal Image

Mercurial Pretender

How it works

1. Put any nontoken creature onto the battlefield.
2. When the creature enters, Radiant Solar, Mercurial Pretender and Phantasmal Image each trigger.
3. Resolve the Radiant Solar trigger, causing you to venture into Tomb of Annihilation and into the Trapped Entry room, causing each player to lose 1 life.
4. Resolve the Mercurial Pretender trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Radiant Solar.
5. Resolve the Phantasmal Image trigger, venturing into the Cradle of the Death God room, creating a 4/4 legendary The Atropal creature token and completing Tomb of Annihilation.
6. If you control two or more The Atropal tokens, put all but one into your graveyard due to the legend rule.
7. Sefris' second ability triggers, returning Radiant Solar from your graveyard to the battlefield.
8. Repeat from step 2.

This loop transforms a single creature entry into a relentless cycle through the Tomb of Annihilation, fueled by clever cloning. As creatures enter and trigger effects, Radiant Solar continuously ventures into the dungeon while Phantasmal Image and Mercurial Pretender copy it to push you rapidly through each room. This culminates in creating The Atropal token in the Cradle of the Death God, which immediately triggers the legend rule if you control two, sending one to the graveyard. That death neatly satisfies Sefris of the Hidden Ways' second ability—her "Create Undead" completion bonus—allowing you to fish Radiant Solar right back out of the graveyard to the battlefield to do it all over again.