Sephiroth, Planet's Heir, Agatha's Soul Cauldron, and Triskelion

Prerequisites

• Sephiroth, Planet's Heir on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Triskelion in exile

Steps

1. If needed, give Sephiroth deathtouch
2. Activate Sephiroth using Triskelion's ability by removing a +1/+1 counter from it, dealing 1 damage to a creature an opponent controls and destroying it due to Sephiroth's deathtouch
3. When the creature dies, Sephiroth triggers, putting a +1/+1 counter on it
4. Repeat from step 2

Results

• Destroy all creatures that enter the battlefield under an opponent's control
• Destroy all creatures opponents control