Trapjaw Kelpie, Carrion Feeder, and Hardened Academic

Prerequisites

• Trapjaw Kelpie on the battlefield
• Carrion Feeder on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Carrion Feeder by sacrificing Trapjaw Kelpie
2. When Trapjaw Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Hardened Academic triggers, putting a +1/+1 counter on Trapjaw Kelpie
4. Resolve the Carrion Feeder ability
5. Repeat

Results

• Infinite +1/+1 counters on a creature
• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers