Undead Knights (and other elite mobs)

Strongholds are large structures that house the portal to The End, that doesn't mean anything though when it's just your basic mobs roaming around. Which is why there needs to be a reason to actually explore these structures. A mob that knows how to block, lunge, dodge, and be a worthy opponent to face you and your diamond armor. Undead archers with status effected arrows and increased speed, or even an Undead necromancer that can summon zombies and skeletons would bring interest back into the game.