Mortuary + Bolas's Citadel + Panicked Bystander // Cackling Culprit + Myr Scrapling

Mortuary

Bolas's Citadel

Panicked Bystander // Cackling Culprit

Myr Scrapling

How it works

1. Activate Myr Scrapling by sacrificing it.
2. When Myr Scrapling dies, Mortuary and Panicked Bystander // Cackling Culprit trigger.
3. Resolve the Mortuary trigger, putting Myr Scrapling from your graveyard onto the top of your library.
4. Resolve the Panicked Bystander // Cackling Culprit trigger, causing you to gain 1 life
5. Resolve the Myr Scrapling ability.
6. Cast Myr Scrapling from the top of your library by paying 1 life.
7. Repeat.

This clever loop turns a tiny mechanical automaton into an infinite engine by leveraging life as a resource in place of mana. With Bolas's Citadel allowing you to cast spells directly from the top of your library, you can repeatedly deploy Myr Scrapling by paying just 1 life instead of its mana cost. Each time you sacrifice Myr Scrapling to its own ability, Mortuary immediately catches it on its way to the graveyard and slides it right back onto the top of your library. Meanwhile, Panicked Bystander // Cackling Culprit sits back and cushions the cost by granting you life every time a creature dies, offsetting the life you spent to recast the artifact creature through the Citadel.