I was thinking of warlock/demon summoner/ shapeshifter before we saw the demon child merc. My other two ideas are fallen paladin/death knight class like from wow. Using decay, blood and frost as a heavy armored meele class vs the necros summon class.
An additonally cool class would be a shinobi/ samurai class. Like a ronin/ ninja / shogun armor varient.
Anything new to flesh out the game and provide fresh content and lore.