Cathars' Crusade, and Yahenni, Undying Partisan

Prerequisites

• Cathars' Crusade on the battlefield
• Yahenni, Undying Partisan on the battlefield

Steps

1. Activate Yahenni by sacrificing the persist creature
2. When the persist creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. When the persist creature enters, Cathars' Crusade triggers, putting a +1/+1 counter on each creature you control
4. Resolve the Yahenni ability
5. Repeat

Results

• Infinite +1/+1 counters on most creatures you control
• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers