Cass, Hand of Vengeance, Phantom Train, and Historian's Boon

Prerequisites

• Cass, Hand of Vengeance on the battlefield
• Phantom Train on the battlefield
• Historian's Boon on the battlefield

Steps

1. Activate Phantom Train by sacrificing another creature that has an Aura attached to it
2. When the creature dies, Cass triggers, returning an Aura that was attached to the creature from your graveyard to the battlefield attached to another creature you control
3. When the Aura enters the battlefield, Historian's Boon triggers, creating a creature token
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