Ashnod's Altar, Grazing Kelpie, and Hardened Academic

Prerequisites

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

Steps

1. Activate Ashnod's Altar by sacrificing Grazing Kelpie
2. When Grazing 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 Grazing Kelpie
4. Repeat

Results

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