Trapjaw Kelpie, Yahenni, Undying Partisan, and Hardened Academic

Prerequisites

• Trapjaw Kelpie on the battlefield
• Yahenni, Undying Partisan on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Yahenni 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 Yahenni ability
5. Repeat

Results

• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers