Mortuary + Phyrexian Altar + Bolas's Citadel + Fear of Lost Teeth

Mortuary

Phyrexian Altar

Bolas's Citadel

Fear of Lost Teeth

How it works

1. Activate Phyrexian Altar by sacrificing Fear of Lost Teeth.
2. When Fear of Lost Teeth dies, it and Mortuary triggers.
3. Resolve the Mortuary trigger, putting Fear of Lost Teeth from your graveyard onto the top of your library.
4. Resolve the Fear of Lost Teeth trigger, causing you to gain 1 life and dealing 1 damage to any target.
5. Cast Fear of Lost Teeth from the top of your library by paying 1 life due to Bolas's Citadel.
6. Repeat.

This engine turns the top of your library into an endless loop by uniting life-payment with instant recycling. With Bolas's Citadel letting you cast creatures right off the library for life instead of mana, you can sacrifice Fear of Lost Teeth to Phyrexian Altar to generate colored mana while triggering its death ability. That death triggers Mortuary, which immediately places Fear of Lost Teeth back on top of your library so Bolas's Citadel can cast it all over again. Because Fear of Lost Teeth actually gains you life when it dies, it completely offsets the life cost required by Bolas's Citadel, letting you cycle the loop infinitely for endless mana, damage, and death triggers.