Radiant Solar + Sefris of the Hidden Ways + Phantom Steed + Underdark Explorer

Decks

How it works

Cast Phantom Steed by paying its mana cost.
When Phantom Steed enters, it and Radiant Solar trigger.
Resolve the Phantom Steed trigger, exiling Underdark Explorer until Phantom Steed leaves the battlefield.
Resolve the Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Phantom Steed.
Phantom Steed leaves the battlefield, causing Underdark Explorer to be returned to the battlefield from exile.
When Underdark Explorer enters, it and Radiant Solar trigger.
Resolve the Underdark Explorer 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 Phantom Steed from your graveyard to the battlefield.
When Phantom Steed enters, it and Radiant Solar trigger.
Resolve the Phantom Steed trigger, exiling Underdark Explorer until Phantom Steed 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 Phantom Steed.
Repeat from step 5.

In which brackets is this combo allowed, per Spellbook's Exhibition tier?

1–2 · Exhibition & Core

Allowed in this bracket.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.

How it works

Cast Phantom Steed by paying its mana cost.
When Phantom Steed enters, it and Radiant Solar trigger.
Resolve the Phantom Steed trigger, exiling Underdark Explorer until Phantom Steed leaves the battlefield.
Resolve the Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Phantom Steed.
Phantom Steed leaves the battlefield, causing Underdark Explorer to be returned to the battlefield from exile.
When Underdark Explorer enters, it and Radiant Solar trigger.
Resolve the Underdark Explorer 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 Phantom Steed from your graveyard to the battlefield.
When Phantom Steed enters, it and Radiant Solar trigger.
Resolve the Phantom Steed trigger, exiling Underdark Explorer until Phantom Steed 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 Phantom Steed.
Repeat from step 5.