Thanks to Jonathan Green and Ikaros for their suggestions. My list of villains now looks like this:
|Why didn’t you choose me?|
Necklace of Skulls
The Overlord (from the Citadel of Chaos by JamieThomson)
The Sorcerer (Siege of Sardath)
Vonotar the traitor
The only one I am doubtful of now is Y. If I can’t find any better alternative, I’ll look for instances where you fight yourself in gamebooks or I could interpret that the mercenary leader in the Crimson Tide is yourself if you had submitted to your ferocity or I could look at instances where you can make really stupid decisions to get yourself killed and so you are your own worst enemy.