Nim Deathmantle + Ashnod's Altar + Merrow Skyswimmer

Nim Deathmantle

Ashnod's Altar

Merrow Skyswimmer

How it works

1. Activate Ashnod's Altar by sacrificing Merrow Skyswimmer, adding CC.
2. When Merrow Skyswimmer dies, Nim Deathmantle triggers, causing you to pay 4 to return Merrow Skyswimmer from your graveyard to the battlefield and attach Nim Deathmantle to it.
3. When Merrow Skyswimmer enters, it triggers, creating a creature token.
4. Activate Ashnod's Altar by sacrificing a creature token, adding CC.
5. Repeat.