Thran Vigil, and Hammerhead, Maggia Boss

Prerequisites

• Thran Vigil on the battlefield
• Hammerhead, Maggia Boss on the battlefield

Steps

1. Activate Hammerhead by sacrificing the creature with persist
2. When that creature 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 that creature
4. Remove a +1/+1 counter and a -1/-1 counter from that creature as a state-based action
5. Resolve the Hammerhead ability from step 1
6. Repeat

Results

• Infinite +1/+1 counters on a creature
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers