Pink Horror + Nim Deathmantle + Ashnod's Altar

Steps

1. Activate Ashnod's Altar by sacrificing Pink Horror, adding {C}{C}.
2. Pink Horror dies, triggering itself and Nim Deathmantle.
3. Resolve the Pink Horror trigger, creating two 2/2 Blue Horror creature tokens.
4. Activate Ashnod's Altar by sacrificing a Blue Horror, adding {C}{C}.
5. Resolve the Nim Deathmantle trigger from step 2, paying {4} to return Pink Horror from your graveyard to the battlefield and attach Nim Deathmantle to it.
6. Repeat.
7. Once you have infinite Blue Horror tokens, you may cast an instant or sorcery spell to deal infinite damage to any number of targets.