Warden of the Grove, and Phantom Train

Prerequisites

• Warden of the Grove on the battlefield
• Phantom Train 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, Warden of the Grove triggers, putting a +1/+1 counter on the persist creature
4. Resolve the Phantom Train ability
5. Repeat

Results

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