Sun Titan + Nim Deathmantle + another nontoken creature with cmc 3 or less
+ Ashnod's Altar = infinite sacrifices and ETBs
+ Ashnod's Altar = infinite sacrifices and ETBs
How it works:
- Sacrifice Sun Titan and another nontoken creature with cmc 3 or less to Ashnod's Altar, making 4 colorless mana and triggering Nim Deathmantle's ability
- Pay 4 to return Sun Titan to the battlefield attached to Nim Deathmantle using Nim Deathmantle's triggered ability
- Return any creature with cmc 3 or less from your graveyard to the battlefield with Sun Titan's ETB ability
- Repeat