Discord has fourth wall awareness and reality warping . He can easily discover superman's weakness to kryptonite and use his reality warping or time manipulation to create genuine gold kryptonite to wound and kill superman . Not only that but Discord is the embodiment of chaos so that means he'll be difficult to put down .Discord could also erase the sun which could deprive superman of his powers. He's also very vulnerable to magic and well discord is a magical being . Superman is not only gonna die to discord ,he's gonna have his soul sent to darkseid in a jar as a gift hahaha .