Aerie Ouphes

If Aerie Ouphes has no -1/-1 counters on it when you sacrifice it to activate its first ability, persist will return Aerie Ouphes to the battlefield with a -1/-1 counter on it before that ability resolves. The ability will check the power of Aerie Ouphes at the time you sacrificed it, not the power of the returned Aerie Ouphes (which is actually a new object with no relation to its previous existence).

The persist ability triggers when the permanent is put into a graveyard. Its last known information (that is, how the creature last existed on the battlefield) is used to determine whether it had a -1/-1 counter on it.

If a creature with persist that has +1/+1 counters on it receives enough -1/-1 counters to cause it to be destroyed by lethal damage or put into its owner’s graveyard for having 0 or less toughness, persist won’t trigger and the card won’t return to the battlefield. That’s because persist checks the creature’s existence just before it leaves the battlefield, and it still has all those counters on it at that point.