The Great Goblin + Amoeboid Changeling + War Elemental

The Great Goblin

Amoeboid Changeling

War Elemental

How it works

1. Activate Amoeboid Changeling by tapping it, causing War Elemental to gain all creature types 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, Orc and Army due to Amoeboid Changeling, dealing 2 damage to an opponent.
4. War Elemental triggers, putting a +1/+1 counter on it.
5. Repeat from step 3.