Spark Double, Putrid Goblin, and Ashnod's Altar

Prerequisites

• Spark Double on the battlefield
• Putrid Goblin on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Ashnod's Altar by sacrificing Spark Double, adding
2. When Spark Double dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. As Spark Double enters the battlefield, choose to have it enter the battlefield as a copy of Putrid Goblin with a +1/+1 counter on it
4. Repeat

Results

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