@Riot, Karthus bug
I'm writing here on NA because on EUW nobody cared about this, Riot didn't even see it probably so..anyway. I believe Karthus is bugged, and the bug is on his E VFX.
This is how it should look like (ghosts around him whenever activated) http://bigdeepzdotcom.files.wordpress.com/2014/05/sdfsdfsdfdsf.png
This is how it actually looks ingame http://i61.tinypic.com/15q99qd.png
It stays so all the game, it seems that build/level doesn't change anything
Also, the ghosts are shown ONLY if you go into Death defied mode without having your E on when you were dying