#4 Superman – Superboy-Prime
Superboy-Prime was originally from Earth Prime, where superheroes were just stories (which was supposed to represent our Earth). The childhood escape from Krypton remains from the original Superman story (albeit with a few tweaks), but in this version Superboy-Prime doesn’t have any powers. Plus, in what amounts to naming a kid “Katniss” or “Khaleesi” in the real world, his adoptive parents Jerry and Naomi Kent named their child “Clark” after the comic book hero Clark Kent, a.k.a. Superman.
Superboy-Prime eventually gained powers and left his dimension. But with time he grew selfish and became a villain. He would make a great villain for future seasons of Legends of Tomorrow or The Flash.
#4 Batman – Vampire Batman
Yes, in one alternate universe there is a vampire version of Batman. Batman becomes a vampire to defeat Dracula, but this later backfires and he kills off almost everyone in the Bat-universe. If the CW wanted to show an alternate timeline gone horribly wrong, this would be one great option.