I feel like Sorcerer's bestowing sentience upon inanimate objects with vague 'magic' is a bad idea.
I feel like you would be cheating your audience if the lore for
was simply "generic evil doll was a generic regular doll before an evil magician brought it to life with magic". I think there's potentially room for one anti-Galio champion (Galio absorbs & nullifies magic; and anti-Galio champion would absorb & channel magic) but I really don't think Shaco or Fiddlesticks would work as that champion.
I think you greatly diminish their ability to interact with the world and, more importantly, characters around them if they have such a binary backstory. I feel just making them some sort of ancient demon gives the lore team more of something to work with. But there are so many better options than just 'Magical living puppet/scarecrow'.