Retribution of the Ancients, Phyrexian Altar, and Hound of Griselbrand

Prerequisites

• Retribution of the Ancients on the battlefield
• Phyrexian Altar on the battlefield
• Hound of Griselbrand on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Hound of Griselbrand, adding
2. Hound of Griselbrand 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 Hound of Griselbrand, giving any creature -1/-1 until end of turn
4. Repeat

Results

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