Ashnod's Altar, Lingering Tormentor, and Hardened Academic

Prerequisites

• Ashnod's Altar on the battlefield
• Lingering Tormentor on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Lingering Tormentor
2. When Lingering Tormentor 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 Lingering Tormentor
4. Repeat

Results

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