Infinite creature LTBInfinite creature ETBInfinite creature sacrifice triggersInfinite death triggersInfinite red mana
How it works
Activate Thermopod's second ability by sacrificing The Master, adding .
When The Master dies, if it was a copy of the undying creature, its undying ability triggers, returning it from your graveyard to the battlefield as a copy of the persist creature with a +1/+1 counter on it.
Otherwise, if The Master was a copy of the persist creature, its persist ability triggers, returning it from your graveyard to the battlefield as a copy of the undying creature with a -1/-1 counter on it.