Karthus needs some changes
Yes, he is unique. Yes, he should squishy
No, he should not die to nearly any champion that sneezes his way. Currently, Karthus feels weak because at no point in the game can he be reliably safe. He is very weak because he can get towered dived so easily due to his no CC, low HP kit
It's no wonder this champion is barely played despite being quite unique and fun to play
dash out flawlessly because every high damage champ needs a dash
simply is not that kind of champion you want to first pick