Mortuary + Gray Merchant of Asphodel + Bolas's Citadel + Phantom Train

Mortuary

Gray Merchant of Asphodel

Bolas's Citadel

Phantom Train

How it works

1. Cast Gray Merchant either from your hand by paying 3 or from the top of your library by paying 5 life.
2. When Gray Merchant enters, it triggers, causing each opponent to lose life equal to your devotion to black and causing you to gain life equal to the life lost this way.
3. Activate Phantom Train by sacrificing Gray Merchant.
4. When Gray Merchant dies, Mortuary triggers, putting Gray Merchant from your graveyard onto the top of your library.
5. Resolve the Phantom Train ability.
6. Repeat.

This elegant loop turns the continuous life payment of Bolas's Citadel into a self-sustaining engine by utilizing Phantom Train's sacrifice ability to repeatedly bin Gray Merchant of Asphodel. Every time the Merchant dies, Mortuary steps in to bypass the graveyard entirely, instantly placing the creature back on top of your library so Bolas's Citadel can cast it again for life instead of mana. Because Gray Merchant of Asphodel's devotion-based drain outpaces the life paid to cast it, you continuously drain your opponents to death while endlessly recycling the Merchant with Phantom Train and Mortuary.