Mortuary + Aetherflux Reservoir + Bolas's Citadel + Phantom Train

Mortuary

Aetherflux Reservoir

Bolas's Citadel

Phantom Train

How it works

1. Activate Phantom Train by sacrificing a creature
2. When the creature dies, Mortuary triggers, putting the creature from your graveyard onto the top of your library.
3. Resolve the Phantom Train ability.
4. Cast the creature from the top of your library by paying X life, where X is the creature's mana value.
5. Aetherflux Reservoir triggers, causing you to gain 1 life for each spell you've cast this turn.
6. Repeat.

This clever engine sets up a seamless loop by utilizing Bolas's Citadel to cast creatures directly off the top of your library for life instead of mana. When you activate Phantom Train to sacrifice one of those creatures, Mortuary instantly catches it on the way to the graveyard, placing the card right back onto the top of your library so Bolas's Citadel can play it again. As you continuously cast and sacrifice your creature to feed Phantom Train's growth, Aetherflux Reservoir steadily outpaces the life cost by gaining you more and more life with each iteration, eventually letting you cash out that massive life total to blast any target for 50 damage.