Mortuary + Bolas's Citadel + Haywire Mite + Yahenni, Undying Partisan

Mortuary

Bolas's Citadel

Haywire Mite

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Haywire Mite.
2. When Haywire Mite dies, it and Mortuary triggers.
3. Resolve the Mortuary trigger, putting Haywire Mite from your graveyard onto the top of your library.
4. Resolve the Haywire Mite trigger, causing you to gain 2 life
5. Resolve the Yahenni ability.
6. Cast Haywire Mite from the top of your library by paying 1 life due to Bolas's Citadel.
7. Repeat.

This elegant loop turns the life-paying drawback of Bolas's Citadel into an engine for infinite value, letting you recast the same creature endlessly off the top of your library. Whenever you use Yahenni, Undying Partisan to sacrifice Haywire Mite, Haywire Mite's own death trigger cushions your life total by netting you 2 life, easily offsetting the 1 life you pay to cast it again. Meanwhile, Mortuary steps in to ensure Haywire Mite never truly stays in the graveyard, instantly placing it right back on top of your library so Bolas's Citadel can play it once more.