Mortuary + Cauldron Familiar + Bolas's Citadel + Thermopod

Mortuary

Cauldron Familiar

Bolas's Citadel

Thermopod

How it works

1. Cast Cauldron Familiar either from your hand or from the top of your library by paying or 1 life respectively.
2. When Cauldron Familiar enters, it triggers, causing each opponent to lose 1 life and you to gain 1 life.
3. Activate Thermopod by sacrificing Cauldron Familiar.
4. When Cauldron Familiar dies, Mortuary triggers, putting Cauldron Familiar from your graveyard onto the top of your library.
5. Repeat.

This loop sets up a self-sustaining engine right off the top of your library, fueled by Bolas's Citadel allowing you to cast spells without paying their mana costs. Whenever you cast Cauldron Familiar, its entry triggers life loss and gain, and you can immediately sacrifice it to Thermopod for red mana. That death triggers Mortuary, which neatly recycles the cat back to the top of your library so Bolas's Citadel can play it all over again.