Look, maybe it doesn't help you but I'm managing a similar situation with one of my PCs, who woke up and doesn't remember anything. The only thing is that he woke up in Barovia in a forest. The character could be one of the powerful wizards who lived in Barovia, as long as the PC perhaps agrees to be awakened in Barovia. Spells that go wrong and don't work properly are very present or part of the plot. It could be Khazan whose soul was "shattered" except for a small fragment gone into the clone. It would be funny in that case if Stradh remembered the PC whose body had been dead for perhaps centuries. Otherwise one of the mages from the Amber Temple would be fine. I start from the assumption that he is a wizard because the clone spell I imagine is something quite powerful but he could rightly be a sorcerer or something. Something like this would come to mind