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

Near-infinite creature ETB

Near-infinite creature LTB

Near-infinite death triggers

Near-infinite lifeloss for all players

Near-infinite creature sacrifice triggers

Radiant Solar

Sefris of the Hidden Ways

Caves of Chaos Adventurer

Mardu Siegebreaker

Cast Fiend Hunter by paying its mana cost.
When Fiend Hunter enters, it and Radiant Solar trigger.
Resolve the Fiend Hunter trigger, exiling Caves of Chaos Adventurer.
Resolve the Radiant Solar trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice Fiend Hunter.
When Fiend Hunter dies, it triggers, returning Caves of Chaos Adventurer from exile to the battlefield.
When Caves of Chaos Adventurer enters, it and Radiant Solar trigger.
Resolve the Caves of Chaos Adventurer 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 Fiend Hunter from your graveyard to the battlefield.
When Fiend Hunter enters, it and Radiant Solar trigger.
Resolve the Fiend Hunter trigger, exiling Caves of Chaos Adventurer.
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 Fiend Hunter.
Repeat from step 5.

Fiend Hunter

Complete a dungeon.
Sefris' second ability triggers twice due to Delney.
Resolve the first trigger, returning up to one other creature from your graveyard to the battlefield.
Resolve the second trigger, returning Caves of Chaos Adventurer from your graveyard onto the battlefield.
When Caves of Chaos Adventurer enters, it triggers once and Preston triggers twice due to Delney.
Holding priority, activate Woe Strider by sacrificing Caves of Chaos Adventurer.
Resolve a Preston trigger, creating a token copy of Caves of Chaos Adventurer that is a 0/1 Illusion.
When the Caves of Chaos Adventurer token enters, it triggers twice due to Delney.
Resolve the Caves of Chaos Adventurer token triggers, venturing into Undercity twice.
Resolve the second Preston trigger from step 5, creating a token copy of Caves of Chaos Adventurer that is a 0/1 Illusion.
Repeat steps 8 and 9 one additional time.
Resolve the Caves of Chaos Adventurer trigger from step 5, venturing into Undercity and completing Undercity.
Repeat from step 2.

Combos with "Caves of Chaos Adventurer"