Young Wolf dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate
Ashnod's Altar by sacrificing
Young Wolf.
When
Young Wolf dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Young Wolf enters and dies as a state-based action due to having 0 toughness. Its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Repeat from step 3.
Notes
If
Young Wolf starts with a +1/+1 counter on it, then you may start the combo from step 3 instead.
Results
Infinite creature ETB.
Infinite creature LTB.
Infinite colorless mana.
Infinite death triggers.
Infinite creature sacrifice triggers.
Metadata
Bracket tag
SpicyBracket 3-4+
Probably 3 or 4, but hard to classify
1
2
3
4
5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.