Liberally copied from World of Warcraft Death Knights, I've employed these as abilities available to Delecti's Dead Captains, powerful undead leaders of his forces.
IMG there were 4: one Captain each of Blood, Frost, and Plague, and a General with all of them. Each logically had access to their 'school' of abilities as well as general ones. They each had a handful of Lieutenants whoe were mostly generalists with maybe one or two category abilities.
Note to GMs: there's a fair amount of 'tracking stuff going on' with a lot of their abilities that happen over ticks of time, or happen/end when triggers go off, so I *recommend* for your sanity employing small numbers of the abilities or only one of the Captains. Not sure how I would have ever kept track of the General if I'd had to.