By Mortarch of Sacrament (Steam Workshop page)
This mod adds in scrap upgrades for the Tomb Kings using Canopic Jars. Each of the four main Tomb King factions have unique upgrades which cost 100 jars, in addition to a plethora of upgrades for the Tomb King roster, ranging from 30 - 80 jars.
I'm currently working on a few submods so I'll get the upgrades listed here as soon as possible!