Cauldron of Souls + Dross Scorpion + Encroaching Mycosynth + Phantom Train

UB identity

Commander legal

The 4 combo pieces

• Cauldron of Souls
• Dross Scorpion
• Encroaching Mycosynth
• Phantom Train

How to execute it

1. Activate Cauldron of Souls by tapping it, giving the creature with bloodthirst persist until end of turn.
2. Activate Phantom Train by sacrificing the creature with bloodthirst.
3. When the creature dies, its persist ability and Dross Scorpion trigger.
4. Resolve the persist trigger, returning the creature from your graveyard to the battlefield, which enters the battlefield with at least one +1/+1 counter on it due to its bloodthirst ability.
5. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
6. Resolve the Phantom Train ability
7. Repeat.

What the combo produces

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