Nim Deathmantle + Ashnod's Altar + Knight of Sorrows

Nim Deathmantle

Ashnod's Altar

Knight of Sorrows

How it works

1. Activate Ashnod's Altar by sacrificing Knight of Sorrows, adding CC.
2. When Knight of Sorrows dies, its afterlife ability and Nim Deathmantle trigger.
3. Resolve the Knight of Sorrows trigger, creating a 1/1 Spirit creature token.
4. Activate Ashnod's Altar by sacrificing the Spirit, adding CC.
5. Resolve the Nim Deathmantle trigger from step 2, causing you to pay 4 to return Knight of Sorrows from your graveyard to the battlefield, and attach Nim Deathmantle to it.
6. Repeat.