The majority of the bosses are only a challenge because they're either just fast or have high HP(some can spawn other bosses or “stop time" but, those are the most unique mechanics for bosses.
Instead of the same high HP slop or cheap mechanics(they're not bad, but overused)
Maybe instead give the bosses better abilities and animations
Like maybe Itachi can use a genjutsu where there are multiple Itachi's and only one of them is real or he disguises as a normal mob
Or Brandon(Mob) as a boss can maybe lift up units and place them somewhere else by moving the ground beneath them