When the Persist Creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it and at least one +1/+1 counter on it due to
Rhythm of the Wild.
Remove a -1/-1 counter and a +1/+1 counter from that creature as a state-based action.
Resolve the
Grimgrin ability.
Repeat.
Results
Infinite +1/+1 counters on a creature.
Infinite creature ETB.
Infinite creature LTB.
Infinite creature sacrifice triggers.
Infinite death triggers.
Metadata
In 52 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Oddball (Bracket 2-3+).