How about making Mordekaiser...

A sustained damage Juggernauth that is nearly unCCable?

It fits a lot into the image of the "Heavy Armored Juggernaut of Death", offers a unique kind of character that won't need mobility simply because he doesn't suffer CCs (not as Olaf Ulti that makes him immune nor like Irelia passive that works with team mates). His damage will be coming from the combo of his skills making enemies more subsceptible to his damage the more he "harvests" them so that he still needs his team to keep them close enough to kill them but isn't toally useless and a one trick pony.