Tephraderm + Hive Mind + Star of Extinction + Quest for Pure Flame

Tephraderm

Hive Mind

Star of Extinction

Quest for Pure Flame

How it works

1. Give Tephraderm indestructible, if needed.
2. Activate Quest for Pure Flame by removing four quest counters from it and sacrificing it, doubling the damage sources you control deal this turn.
3. Cast Star of Extinction by paying 5.
4. Hive Mind triggers, causing each opponent to copy Star of Extinction.
5. Resolve an opponent's Star of Extinction, destroying a land and dealing 20 damage to each creature and planeswalker.
6. Tephraderm's second ability triggers, dealing 40 damage to the opponent who controlled the Star of Extinction copy due to Quest for Pure Flame.
7. Repeat from step 5 for each remaining Star of Extinction until each opponent loses the game.