New Karthus skin
I was thinking that we could have something like a Harry Potter Karthus skin (not necessarily by that name). There would be no nose and his eyes would be red. Instead of a book he could have something like the elder wand and his cloak could be shimmering like the invis cloak. Another awesome thing is his quotes. For his ulti he could shout avada kadavera and if he uses his q he could pretend to aim with the wand.
Also for his recall animation he could pretend to apparate by spinning around before landing on the platform. For his joke he could pretnd to cover himself with the cloak and say 'oh i guess im not invisible.'
And he could laugh and call somebody a mudblood for his taunt. Finally if he dies he could hold a resurrection stone above him for a few seconds Just an idea :D*[slayer-jinx-wink]*