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

Mortuary

Crimson Kobolds

Bolas's Citadel

Yahenni, Undying Partisan

How it works

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

This clever loop transforms free sacrifice into a self-sustaining engine by turning the top of your library into an endless hand. With Bolas's Citadel allowing you to cast spells directly from your library by paying life instead of mana, you can deploy Crimson Kobolds for free since its mana value is zero. Once the Kobolds hit the battlefield, you sacrifice them to Yahenni, Undying Partisan, whose ability protects itself while sending the creature to the graveyard. That death immediately triggers Mortuary, which places the Crimson Kobolds right back on top of your library, perfectly positioned for Bolas's Citadel to cast them all over again.