Sefris of the Hidden Ways + Radiant Solar + Gigantoplasm + Synth Infiltrator

Sefris of the Hidden Ways

Radiant Solar

Gigantoplasm

Synth Infiltrator

How it works

1. Put any nontoken creature onto the battlefield.
2. When the creature enters, Radiant Solar, Synth Infiltrator and Gigantoplasm 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 Synth Infiltrator trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Radiant Solar.
5. Resolve the Gigantoplasm 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 relies on Sefris of the Hidden Ways and Radiant Solar working in tandem to rapidly plow through the Tomb of Annihilation dungeon the moment any creature enters the battlefield. As the triggers resolve, Synth Infiltrator and Gigantoplasm enter as copies of Radiant Solar to compound the dungeon progress, ultimately completing it and triggering Sefris of the Hidden Ways's "Create Undead" ability. This final payoff snags Radiant Solar right back out of the graveyard and puts it back onto the battlefield, resetting the entire engine to endlessly repeat your near-infinite loop of sacrifices, life loss, and dungeon excursions.