Retribution of the Ancients, Phyrexian Altar, and Vengeful Vampire

Prerequisites

• Retribution of the Ancients on the battlefield
• Phyrexian Altar on the battlefield
• Vengeful Vampire on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Vengeful Vampire, adding
2. Vengeful Vampire dies, triggering its undying ability, 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 Vengeful Vampire, giving any creature -1/-1 until end of turn
4. Repeat

Results

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