Geralf, the Fleshwright + Putrid Goblin + Grimgrin, Corpse-Born

Geralf, the Fleshwright

Putrid Goblin

Grimgrin, Corpse-Born

How it works

1. Activate Grimgrin by sacrificing Putrid Goblin.
2. When Putrid Goblin dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When Putrid Goblin enters the battlefield, Geralf's second ability triggers, putting a number of +1/+1 counters on it equal to the number of other Zombies that entered the battlefield under your cotnrol this turn.
4. Resolve the Grimgrin ability
5. Repeat.