Athreos, Shroud-Veiled, Blue, Loyal Raptor, and Grimgrin, Corpse-Born

Prerequisites

• Athreos, Shroud-Veiled on the battlefield
• Blue, Loyal Raptor on the battlefield
• Grimgrin, Corpse-Born on the battlefield

Steps

1. Cast the Dinosaur in your hand by paying its mana cost
2. It will enter with a coin counter due to Blue
3. Activate Grimgrin by sacrificing the Dinosaur
4. When the Dinosaur dies, Athreos's second ability triggers, returning the Dinosaur from your graveyard to the battlefield
5. It will enter with a coin counter due to Blue
6. Resolve the Grimgrin ability
7. Repeat from step 2

Results

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