Mortuary + Cauldron Familiar + Bolas's Citadel + Phyrexian Altar

Mortuary

Cauldron Familiar

Bolas's Citadel

Phyrexian Altar

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 Phyrexian Altar 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 elegant loop transforms life into a relentless engine by turning Bolas's Citadel's alternative life-payment cost into a renewable resource. With Bolas's Citadel allowing you to cast Cauldron Familiar directly from the top of your library, the cat enters the battlefield to drain your opponents and heal you. You then feed Cauldron Familiar to Phyrexian Altar to generate the black mana needed to recast it, while Mortuary instantly catches the cat upon its death and places it right back onto the top of your library. The life you gain from each iteration cushions the cost of Bolas's Citadel's spell-casting ability, letting you effortlessly cycle the cat over and over again.