Eternal Scourge, Nightmare Shepherd, and Ashnod's Altar

Prerequisites

• Eternal Scourge on the battlefield
• Nightmare Shepherd on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Eternal Scourge, adding
2. Nightmare Shepherd triggers
3. Resolve the Nightmare Shepherd trigger, exiling Eternal Scourge from your graveyard and creating a 1/1 copy of Eternal Scourge that is a Nightmare in addition to its other types
4. Activate Ashnod's Altar by sacrificing the Eternal Scourge token, adding
5. Cast Eternal Scourge from exile by paying
6. Repeat

Results

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