Valkyrie's Call + Amoeboid Changeling + Spawning Pit + Coercive Recruiter

Valkyrie's Call

Amoeboid Changeling

Spawning Pit

Coercive Recruiter

How it works

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