Mortuary + Bolas's Citadel + Rograkh, Son of Rohgahh + Phantom Train

Mortuary

Bolas's Citadel

Rograkh, Son of Rohgahh

Phantom Train

How it works

1. Activate Phantom Train by sacrificing Rograkh
2. When Rograkh dies, Mortuary triggers, putting Rograkh from your graveyard onto the top of your library.
3. Resolve the Phantom Train ability.
4. Cast Rograkh from the top of your library by paying 0 life.
5. Repeat.

This loop turns the zero-mana cost of Rograkh, Son of Rohgahh into an engine of endless iteration by using Bolas's Citadel to let you cast him straight off the top of your library without paying his mana cost in life. Once he's on the battlefield, you feed him to Phantom Train's activation cost, pumping the Vehicle with a +1/+1 counter while sending Rograkh to the graveyard. That death event immediately wakes up Mortuary, whose static trigger catches Rograkh on his way to the graveyard and places him right back on top of your library, perfectly positioned for Bolas's Citadel to cast him all over again.