The old RPG books had a lot of cool stuff in them, shame most of it got ignored.
The idea of a Prestige Class like in DnD RPGs is neat.

https://warcraft.wiki.gg/wiki/Prestige_class
https://warcraft.wiki.gg/wiki/Scarlet_inquisitor
https://warcraft.wiki.gg/wiki/Dragonsworn
https://warcraft.wiki.gg/wiki/High_divinist
https://warcraft.wiki.gg/wiki/Naga_anomaly