Mordekaiser is really close to being good, but a couple more changes would be nice
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Remove the buddy system; both requiring Morde to hug his allies to deal damage and the XP component. You should probably nerf the cloud to compensate for that, as it would buff the shit out of Junglekaiser. AD Carrykaiser was a horrible mistake, and the mechanics that enabled it have no place on our favorite tin can.
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Give him the base stats of a melee champion. Seriously, Mordekaiser's base HP and Armor are almost as low as Zilean, not to mention 325 movement speed. I can understand the low base HP because of his passive, but he needs to have at least passable armor and movement speed.