Well after beating the king a pretty obvious next step would be killing god (or maybe rather just the pope?)
Priests would be glass cannon, as they could exorcise the "evil" spirits but wouldn't wear armor, which would be easy to beat up if not for the fact that there is a blessing already in the game that works great for glass cannons
You could add templars with lower stats than knights, but with an extra mechanic like their attacks also dealing 1 damage to unit behind the target which would counter summon swarm strats quite a bit, idk tho
You could add inquisition too, both overzealous peasants that would debuff ur units with prayer and die right after, and maybe inquisitors too, specifically capitalizing on that debuff, maybe even spawning the former
Idk tho