Activate Phyrexian Altar by sacrificing Young Wolf, adding ({B} magic symbol) .
Young Wolf dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Retribution of the Ancients by paying ({B} magic symbol) and removing a +1/+1 counter from Young Wolf, giving any creature -1/-1 until end of turn.
Repeat.
Results
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite sacrifice triggers.
Reduce any number of target creatures' toughness to zero.