Cast Worldfire by paying {6}{R}{R}{R}, exiling all permanents, all cards in all hands and graveyards, and setting each player's life total to one.
Outpost Siege triggers for each creature you had leave the battlefield this way.
Resolve the first Outpost Siege trigger, dealing 1 damage to any opponent.
The opponent loses the game due to having zero or less life.
Repeat from step 3 for each remaining opponent.

Each opponent loses the game

Exile all cards in hands and graveyards

Exile all permanents

Near-infinite lifeloss

Mass Land Denial

Worldfire

Outpost Siege

Deal damage to Vrondiss.
Rite of Passage and Vrondiss trigger.
Resolve the Rite of Passage trigger, putting a +1/+1 counter on Vrondiss.
Resolve the Vrondiss trigger, creating a 5/4 Dragon Spirit creature token.
The Dragon Spirit enters the battlefield, triggering Warstorm Surge, causing the Dragon Spirit to deal damage equal to its power to any target.
The Dragon Spirit triggers, causing you to sacrifice it.
The Dragon dies, triggering Outpost Siege, dealing 1 damage to Vronidss.
Repeat from step 2.

Infinite damage

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Vrondiss, Rage of Ancients

Rite of Passage

Warstorm Surge

Deal damage to Vrondiss.
Rite of Passage and Vrondiss trigger.
Resolve the Rite of Passage trigger, putting a +1/+1 counter on Vrondiss.
Resolve the Vrondiss trigger, creating a 5/4 Dragon Spirit creature token.
The Dragon Spirit enters the battlefield, triggering Scourge of Valkas, causing the Dragon Spirit to deal damage equal to the number of Dragons you control to any target.
The Dragon Spirit triggers, causing you to sacrifice it.
The Dragon dies, triggering Outpost Siege, dealing 1 damage to Vronidss.
Repeat from step 2.

Scourge of Valkas

Deal damage to Vrondiss.
Rite of Passage and Vrondiss trigger.
Resolve the Rite of Passage trigger, putting a +1/+1 counter on Vrondiss.
Resolve the Vrondiss trigger, creating a 5/4 Dragon Spirit creature token.
The Dragon Spirit enters the battlefield, triggering Pandemonium, causing the Dragon Spirit to deal damage equal to its power to any target.
The Dragon Spirit triggers, causing you to sacrifice it.
The Dragon dies, triggering Outpost Siege, dealing 1 damage to Vronidss.
Repeat from step 2.

Pandemonium

Combos with "Outpost Siege"