Rendclaw Trow, Phantom Train, and Hardened Academic

Prerequisites

• Rendclaw Trow on the battlefield
• Phantom Train on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Phantom Train by sacrificing Rendclaw Trow
2. When Rendclaw Trow 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 Rendclaw Trow
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