User blog comment:22kingdomheartsfan/Plans for Goku and Superman vs Frieza and Darkseid/@comment-27180367-20180330234901

Much like Goku, Xenoverse gives Frieza a drastic boost in power. Xenoverse gives a huge power boost to the entire cast. And the universe busters in the anime apparently get upgraded to higher dimensions from what I've heard.

So if you're using Xenoverse which gives Goku and Frieza higher dimensional attacking potency, then it's only fair to use a higher dimensional Superman. My pick wour be Strange Visitor. And for Darkseid, I'd pick Anti Life Equation Darkseid who was powerful enough to destroy the source wall which contains the entire infinite DC multiverse.

I'm not 100% sure if that makes it a fair fight, I haven't researched the Xenoverse games fully, but it's the best I can think of right now. Hope this helps