How is Karthus in 2018?

Karthus is just fine.

I went 3/0/8 with him yesterday. But it was a silver game, overall I'd call it a risky pick for low output. Even with Ultimate Cap, his ult cooldown takes a LONG time and you don't get CDR that quickly with him since tear and RoA are basically must takes for him. games are finishing around ~30 minutes. I've had like 2-3 games where in mid I've gotten my full

terrible pick another main.

i personally think he needs a grounded effect on his wall, no other changes

Trash like any other mage.

I like him. Okay early game, really good late game. And because I have the pentakill skin for him, I pretend to rock out every game.