Geralf, the Fleshwright + Putrid Goblin + Phantom Train

Geralf, the Fleshwright

Putrid Goblin

Phantom Train

How it works

1. Activate Phantom Train 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 Phantom Train ability
5. Repeat.