Hapatra, Vizier of Poisons, Cathars' Crusade, and Barrenton Medic

Prerequisites

• Hapatra, Vizier of Poisons on the battlefield
• Cathars' Crusade on the battlefield
• Barrenton Medic on the battlefield
• Barrenton Medic does not have summoning sickness
• Barrenton Medic has less than three -1/-1 counters on it
• It is your turn

Steps

1. Activate Barrenton Medic by tapping it, preventing the next one damage dealt to it this turn
2. Activate Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping it
3. Hapatra triggers, creating a 1/1 Snake creature token
4. The Snake enters the battlefield, triggering Cathars' Crusade, putting a +1/+1 counter on each creature you control
5. Repeat

Results

• Infinite creature tokens
• Infinite ETB
• Infinite +1/+1 counters