I like your ideas, and may have found a way to incorporate one of lakin5's suggestions alongside them. In this man's jealousy over those with superhuman powers (which of course encompasses all manner of supernatural creatures), he creates a means to control electrical currents through some advanced technology. This allows him to control any current, no matter how small or large, and one can imagine the horrifying things this would allow him to do. (Example: your brain sends tiny electrical signals constantly. He finds a way to exploit those and torture you. Yikes.) Given humanity's dependence on electronics these days, I think him having this sort of self-made power could indeed make him a credible threat, and there are probably ways he could use it to deter Clara's telekinesis on him, thus leveling the playing field, if you will. What do you think?
Importantly, this secretive man should have those who know him, who would serve as the people that Clara kills to get to him. One of these people I plan to make an innocent, a classmate and friend of AJ's, and boyfriend of her friend Miranda (tentative name: Derek). He doesn't knowingly end up working for this man; he's a college kid simply looking for a job, and he takes the wrong one. Clara will realize he's an innocent and spare him, but if you know the gory details of the preceding books, you'd know that things probably won't end well for Derek in spite of this. Given the path this story is headed, how do you think these other people could be incorporated?
Also, while a cute idea, naming him Igor and making him Frankenstein's ascended pawn seems tacky and out-of-place for my storyline (though if you want to run with it, go ahead). This would be a man born in the 1950s-1960s, so names for him should be appropriate for that time. I'd like to incorporate historical events from that time period into his backstory, but at the moment I don't know where I would start. Any ideas?