Garza Zol, Plague Queen, Agatha's Soul Cauldron, and Walking Ballista

Prerequisites

• Garza Zol, Plague Queen on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Walking Ballista in exile
• Garza Zol has at least one +1/+1 counter on it
• You have a way to give Garza Zol deathtouch

Steps

1. Give Garza Zol deathtouch, if needed
2. Activate Garza Zol using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to a creature an opponent controls
3. The creature dies as a state-based action due to Garza Zol's deathtouch
4. Garza Zol's first ability triggers, putting a +1/+1 counter on itself
5. Repeat from step 2
6. You may also repeat this combo whenever a creature enters the battlefield under an opponent's control if you can give Garza Zol deathtouch indefinitely

Results

• Destroy all creatures opponents control
• Destroy any creature that enters the battlefield under an opponent's control