Xavier Sal, Infested Captain, Agatha's Soul Cauldron, Hapatra, Vizier of Poisons, and Barrenton Medic

Prerequisites

• Xavier Sal, Infested Captain on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Hapatra, Vizier of Poisons on the battlefield
• Barrenton Medic in exile

Steps

1. Activate Xavier Sal's second ability by tapping it and sacrificing another creature, putting a +1/+1 counter on it
2. Activate Xavier Sal using Barrenton Medic's second ability by putting a -1/-1 counter on it
3. Hapatra triggers, creating a creature token
4. Resolve the Xavier Sal ability, untapping it
5. Repeat

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Infinite creature tokens
• Infinite proliferate