Blightbeetle, Phantom Train, and Harmless Offering

Prerequisites

• Blightbeetle on the battlefield
• Phantom Train on the battlefield
• Harmless Offering in hand
• available

Steps

1. Donate Blightbeetle to an opponent Activate Phantom Train by sacrificing the undying creature
2. When the undying creature dies, its undying ability triggers, returning itself from your graveyard to the battlefield without a +1/+1 counter on it due to Blightbeetle
3. Resolve the Phantom Train ability
4. Repeat from step 2

Results

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