I can get behind casting and then it goes on CD. It'd mean it needs a longer base cooldown though, balanced around the maiden being alive for 20-30 seconds.
Or it can get the cooldown reduced as she's alive down to a cetain point, like maybe an extra 20% CD if she's alive for a minute or something. It'd be a small amount that would rarely ever be reached.
Though I will also say that Yorick does NOT need any buffs. He's pretty well balanced and during that short period where he saw a lot of play, He sat just about around 50% winrate. The only Buff I'd like to see is to the Maiden when Yorick is not there. Maybe something like Ghouls' damage dont fall off if the Maiden is near them. Or she still does full damage even if Yorick isn't near by. Something to help her take towers alone better. Deffinitly does not need a buff when she is near Yorick, it already can feel like a 2v1 when she is there. I can't tell you how many kills I've gotten because someone can almost finish me so the chase, but get killed by the ghouls and her.
Also, quick tip for you. If you've taken their first tower top, you can get maiden to leave lane if you hit either Gromp or Krugs. She'll agro the camp and once it's cleared you can actually back and she'll recall with you. Same trick works for ghouls. Or the glitch where she walks the entire way back happens and she meets you on your way out. Little feels as bad for the opponent as dying to you, and when they see you again, the Maiden is still there.
