Valkyrie's Call + Amoeboid Changeling + Spawning Pit + Deceiver Exarch

Valkyrie's Call

Amoeboid Changeling

Spawning Pit

Deceiver Exarch

How it works

1. Activate Amoeboid Changeling's second ability by tapping it, removing all creature types from Deceiver Exarch.
2. Activate Spawning Pit by sacrificing Deceiver Exarch.
3. When Deceiver Exarch dies, Valkyrie's Call triggers, returning Deceiver Exarch from your graveyard to the battlefield as an Angel with flying and a +1/+1 counter on it.
4. When Deceiver Exarch enters the battlefield, it triggers, untapping Amoeboid Changeling.
5. Resolve the Spawning Pit ability, putting a charge counter on it.
6. Repeat.