Sure, you have your volcano lair and your lava machines, but the real money? Stealing the world’s gold, oil, and anything else valuable that’s underground. Also, some really boring monologues about uniformitarianism. Oh, and dinosaurs. But only kind of.
Making your own skin supernaturally beautiful. Inflicting hideous boils and rashes on those you don’t like. Also, lotion monsters.
Mad optometry (terrifying). You could do a lot of those, actually. Mad dentistry/orthodontics. Mad ear, nose, and throat doctor. Mad statistician. Mad economist.