Retribution of the Ancients, and Phyrexian Altar

Prerequisites

• Retribution of the Ancients on the battlefield
• Phyrexian Altar on the battlefield
• undefined

Steps

1. Activate Phyrexian Altar by sacrificing the undying creature, adding
2. When the undying creature dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
3. Activate Retribution of the Ancients by paying and removing a +1/+1 counter from the undying creature, giving any creature -1/-1 until end of turn
4. Repeat

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Reduce any number of target creatures' toughness to 0