Radiant Solar, Sefris of the Hidden Ways, Phantom Steed, and Seasoned Dungeoneer

Prerequisites

• Radiant Solar on the battlefield
• Sefris of the Hidden Ways on the battlefield
• Phantom Steed in hand
• Seasoned Dungeoneer on the battlefield
• available

Steps

1. Cast Phantom Steed by paying its mana cost
2. When Phantom Steed enters, it and Radiant Solar trigger
3. Resolve the Phantom Steed trigger, exiling Seasoned Dungeoneer until Phantom Steed leaves the battlefield
4. Resolve the Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Phantom Steed
5. Phantom Steed leaves the battlefield, causing Seasoned Dungeoneer to be returned to the battlefield from exile
6. When Seasoned Dungeoneer enters, it and Radiant Solar trigger
7. Resolve the Seasoned Dungeoneer 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 Phantom Steed from your graveyard to the battlefield
10. When Phantom Steed enters, it and Radiant Solar trigger
11. Resolve the Phantom Steed trigger, exiling Seasoned Dungeoneer until Phantom Steed 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 Phantom Steed
14. Repeat from step 5

Results

• Near-infinite ETB
• Near-infinite LTB
• Near-infinite death triggers
• Near-infinite lifeloss for all players
• Near-infinite sacrifice triggers