Sometimes it's not an ability that is op. It's the combination of abilities/stats on the champ that make it op. So please nerf slipped and fanatic.
Don't you dare touch my precious fanatics, what the Firk am I going to do if all 20ish or so of them get nerfed? Still use them? Probably.
My personal favourite Manic champ is Goblin King Carrying Avarice Strength of Body (from Cropsick) Then some other stuff... Leech Vitality (from Gloombringer) One with Nora (from Kaiser) Multi attack (from Archer) Etc
That doesn't sound like the classic goblin king of vulnerability: everything and every minor faction racial.
Hammer time. Manic is crazy strong with tank like fishkisser and if you give flying or teleport then it is more simple to use that stuff. There is item in UD that can give this ability too but with restrictions. I think about two things: Can't touch this or Put drawback like: after 6 rounds it loose manic and have immobile on 3 rounds. Booo nerf you say but in same time: AVARICE - Equipped champion gains Manic. If this item is destroyed then user take immobile on 3 rounds.