Cathars' Crusade, and Aerie Ouphes

Prerequisites

• Cathars' Crusade on the battlefield
• Aerie Ouphes on the battlefield
• An additional creature with flying and indestructible on the battlefield

Steps

1. Activate Aerie Ouphes' ability by sacrificing itself to deal 4 damage to the creature with flying and indestructible
2. Aerie Ouphes's Persist ability triggers, returning Aerie Ouphes from your graveyard to the battlefield with a -1/-1 counter on it
3. Cathars' Crusade triggers, putting a +1/+1 counter on all creatures you control
4. The -1/-1 counter and +1/+1 counter on Aerie Ouphes are removed as a state-based action
5. Repeat

Results

• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers
• Infinite +1/+1 counters