Mordekaiser should get a skin that gives a subtle nod to the old morde's reputation..

I was thinking "Bug King Mordekaiser" Where his armor is made of like spider carapace and his mace is a big ant head on a stick, passive visual effect is a swarm of locust. Give him a few extra voice lanes that are just his old voice lines with the new VO. This of course in reference to the fact that morde had more bugs pre rework than any other champion.

Or...

I also thought of "Spaghetti Monster Mordekaiser" Where him, and his abilities are all replaced with pasta, in reference to his old, spaghetti code.