Umbral Collar Zealot, Heartmender, and Thran Vigil

Prerequisites

• Umbral Collar Zealot on the battlefield
• Heartmender on the battlefield
• Thran Vigil on the battlefield

Steps

1. Activate Umbral Collar Zealot by sacrificing Heartmender
2. When Heartmender dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Thran Vigil triggers, putting a +1/+1 counter on Heartmender
4. Resolve the Umbral Collar Zealot ability
5. Repeat

Results

• Infinite ETB
• Infinite LTB
• Infinite death triggers
• Infinite sacrifice triggers
• Infinite surveil