Ashnod's Altar, Trapjaw Kelpie, and Hardened Academic

Prerequisites

• Ashnod's Altar on the battlefield
• Trapjaw Kelpie on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Ashnod's Altar 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. Repeat

Results

• Infinite creature ETB
• Infinite creature LTB
• Infinite colorless mana
• Infinite death triggers
• Infinite creature sacrifice triggers