serial numbered mtg cards Key to the City | The Brothers' War Retro Artifacts A Collector's Guide to Magic:

Over time, these Thran humans were cured of their ailments by Yawgmoth via a process called phyresis, and in time the entire plane followed suit, becoming a vast mechanical hellscape of blood, metal, and oil where machinery replaced the organic and obedience replaced individualism

I covered the whole process in my article about how important math is to doing the thing in Commander, if you want to read more on that

If you're unfamiliar with these, each came with a 60-card deck built around a particular guild's theme, five double-sided tokens, an official guild pin, a guild sticker, and a spindown life counter

Is it a supertype, a subtype, or neither