Leonardo, Sewer Samurai + Solemnity + Altar of Dementia + Ornithopter

Leonardo, Sewer Samurai

Solemnity

Altar of Dementia

Ornithopter

How it works

1. Activate Altar of Dementia by sacrificing Ornithopter.
2. Cast Ornithopter from your graveyard by paying 0. It will not enter with a finality counter on it due to Solemnity.
3. Repeat.

This loop turns a humble zero-mana artifact into an infinite milling machine by exploiting a clever rules interaction. While Altar of Dementia provides the sacrifice outlet to mill your opponent based on the sacrificed creature's power, Leonardo, Sewer Samurai supplies the crucial recursion engine that lets you recast creatures directly from your graveyard. Normally, casting Ornithopter this way would saddle it with a finality counter, but Solemnity acts as the linchpin that prevents any counters from ever being placed on your creatures, allowing Ornithopter to return to the battlefield entirely unhindered over and over again.