Tephraderm + Hive Mind + Star of Extinction + Furnace of Rath

Tephraderm

Hive Mind

Star of Extinction

Furnace of Rath

How it works

1. Give Tephraderm indestructible, if needed.
2. Cast Star of Extinction by paying 5.
3. Hive Mind triggers, causing each opponent to copy Star of Extinction.
4. Resolve an opponent's Star of Extinction, destroying a land and dealing 40 damage to each creature and planeswalker due to Furnace of Rath.
5. Tephraderm's second ability triggers, dealing 80 damage to the opponent who controlled the Star of Extinction copy due to Furnace of Rath.
6. Repeat from step 4 for each remaining Star of Extinction.