The Great Goblin + Unnatural Selection + War Elemental

The Great Goblin

Unnatural Selection

War Elemental

How it works

1. Activate Unnatural Selection by paying 1, causing War Elemental to become a Goblin until end of turn.
2. Put a counter on War Elemental.
3. The Great Goblin's first ability triggers, as War Elemental is a Goblin due to Unnatural Selection, dealing 2 damage to an opponent.
4. War Elemental triggers, putting a +1/+1 counter on it.
5. Repeat from step 2.