Green Dragon, Overseer of the Damned, and Pandemonium

Prerequisites

• Green Dragon in hand
• Overseer of the Damned on the battlefield
• Pandemonium on the battlefield
• available

Steps

1. Cast Green Dragon by paying
2. Green Dragon enters the battlefield, triggering itself and Pandemonium
3. Resolve the Green Dragon trigger, causing any creature your opponent control that are dealt damage this turn to be destroyed
4. Resolve the Pandemonium trigger, dealing damage equal to Green Dragon's power to any creature an opponent controls
5. Green Dragon triggers, destroying the creature dealt damage
6. The creature dies, triggering Overseer of the Damned's second ability, creating a 2/2 Zombie creature token
7. The Zombie enters the battlefield, triggering Pandemonium, dealing damage equal to the Zombie's power to any creature an opponent controls
8. Repeat from step 5

Results

• Destroy all nontoken creatures opponents control
• Near-infinite creature tokens
• Near-infinite ETB