8. Mister Mxyzptlk
Mister Mxyzptlk has appeared in live-action form in the Superman TV show Smallville, though his appearance was changed completely, sure evidence that bringing this character into the corporeal world is freaking impossible. The villain with the famously difficult-to-pronounce name is a prankster who loves to provoke Supes, and incredulously, the easiest way to get rid of him is simply to trick Mxyzptlk into a condition he lays down at the outset, such as saying his own name backwards or painting his face blue, both of which cause him to be sent back to his home for an indeterminate period (because...magic). The main reason we'll never see him on-screen is that, as far as villains go, he's pretty low on ambition. Mxyzptlk isn't a particularly malicious baddie; he just wants to have some fun and play some tricks, which is just as well, given that if he had the true supervillain mindset, he would be able to ruin Superman with a click of his fingers. Instead, Mxyzptlk has the odd distinction of being the only villain who is actually protective over Superman, because if he wasn't around, he'd have to find another straight-faced goon to play pranks on.