User blog comment:Doeniel/Karthus, the Deathsinger Rework Ideas & Discussion/@comment-8050014-20151206044731

I like the updated ult and W, and especially the passive (very clever). The healing version of the wall is the best, I think. It would help him become a very strong AP jungler with powerful sustain, maybe even on a level with the likes of Fiddlesticks.

I wonder if there is a way to make his ult on epic monsters more interesting to play against, though. I had a thought that maybe to make his ult more balanced it would only activate on epic monsters if an ally was in combat with an enemy who was fighting the monster, to promote a more team-oriented playstyle and to give the enemies another chance to prevent him stealing it (especially if they don't have a Smite, Consume, or Feast up).

Overall good rework, in my opinion. Right now Karthus is boring and somewhat weak, like you said. This would help fix some of his problems while also making him more attractive (not that way) as a champion pick, while also giving him more counterplay.