Mortuary + Phyrexian Altar + Ornithopter + Gwenom, Remorseless

Mortuary

Phyrexian Altar

Ornithopter

Gwenom, Remorseless

How it works

1. Activate Phyrexian Altar by sacrificing Ornithopter
2. When Ornithopter dies, Mortuary triggers, putting Ornithopter from your graveyard onto the top of your library.
3. Cast Ornithopter from the top of your library by paying 0 life.
4. Repeat.

This elegant loop hinges on Mortuary, which quietly ensures that any creature dying from the battlefield goes straight to the top of your library instead of the graveyard. To get this engine turning, you feed Ornithopter to Phyrexian Altar to generate a mana of any color, triggering the enchantment to place the artifact right back on top of your library. From there, Gwenom, Remorseless steps in as the enabler; once she has attacked, her passive ability lets you cast spells from the top of your library by paying life equal to their mana value. Because Ornithopter costs zero mana, its mana value is zero, allowing you to recast it for free without paying any life at all to feed the Altar anew.