Phantom Train, and Rocksteady, Mutant Marauder

Prerequisites

• Phantom Train on the battlefield
• Rocksteady, Mutant Marauder on the battlefield

Steps

1. Activate Phantom Train by sacrificing the persist creature
2. When the persist creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. When the persist creature enters, Rocksteady triggers, putting a +1/+1 counter on that creature
4. Resolve the Phantom Train ability
5. Repeat

Results

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