Superman doesn’t really have that deep of a bench when it comes to villains. The Flash has the Rogues, Batman has all the cool gangsters, and Superman is more or less left with the B-list Joker knockoffs and whoever Luthor is employing to kill him this week. So, if you’re stuck doing a movie franchise, and you don’t want to go back to the Luthor well, you don’t have a ton to work with.
Which is why, at first, Zack Snyder was going to bring perpetual lame-ass Metallo to the silver screen for Batman v Superman: Dawn of Justice. For those who didn’t grow up reading Superman comics, Metallo is a robot with some jerk’s brain in it, and he’s got a Kryptonite heart. That’s it. That’s his shtick. He tries to expose Superman to Kryptonite, and gets his butt kicked, usually after discovering that Superman does not kill, but does not define turning off a robot by removing its power source as killing it.
Thankfully, Snyder admits he came up with the idea of Batman buying some Kryptonite as a credits gag, and soon realized that Superman is the best Batman villain. One assumes Metallo will get his day in the sun, though. It’ll probably be a 5-minute sequence in which he’s beaten like a speedbag by Batman, who was just randomly swinging by, saw the radioactive skull-faced robot, and decided it needed a punching. That’s more or less Metallo in the comics anyway.
(Via Comic Book)