So an arrow fired with great precision through his eye would still take him down? Not that Kis could do that, she's just about good enough to hit a guy in the throat when she was aiming for his head.
Luckily there's now a loaded crossbow lying on the floor for Garen to grab, if he needs it. :)
Since, in this dimension, Adamar can't conjure lighting as powerful as real lightning bolts to overload his armor, that would probably be your best bet. You could also melee fight him if you are good enough or try something fancy, like stabbing though a weak spot and shooting lightning through the metal object, possibly his own lightning from the spear.
