Mortuary + Bolas's Citadel + Crookshank Kobolds + Yahenni, Undying Partisan

Mortuary

Bolas's Citadel

Crookshank Kobolds

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Crookshank Kobolds
2. When Crookshank Kobolds dies, Mortuary triggers, putting Crookshank Kobolds from your graveyard onto the top of your library.
3. Resolve the Yahenni ability.
4. Cast Crookshank Kobolds from the top of your library by paying 0 life.
5. Repeat.

This loop relies on turning a zero-mana creature into a perpetual motion machine fueled by life rather than mana. By using Bolas's Citadel, you can bypass normal casting restrictions to repeatedly cast Crookshank Kobolds straight from the top of your library for free, since its mana value is zero. Yahenni, Undying Partisan provides the necessary sacrifice outlet to send the Kobolds back to the graveyard, while Mortuary catches them on the way down and neatly stacks them right back onto the top of your library.