Grimgrin, Corpse-Born, and Hardened Academic

Prerequisites

• Grimgrin, Corpse-Born on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Grimgrin 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. Hardened Academic 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 Grimgrin 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