Ambitious Dragonborn without a -1/-1 counter on it).
Notable Prerequisites
You control a creature with power X or greater, or you have a creature card in your graveyard with power X or greater.
Steps
Activate
Grimgrin by sacrificing
Ambitious Dragonborn.
When
Ambitious Dragonborn dies, its persist ability triggers, returning it from your graveyard to the battlefield without a -1/-1 counter on it due to its replacement effect.
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 0 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Exhibition (Bracket 1+).