Okay. Imma break this down here and discuss what i think of these specific MUs
Supes
Disadvantage/Heavy Disadvantage(I hate giving specific numbers this early) Superman out zones, out neutrals, out damages and basically just out everythings Red Hood. It's a fairly difficult MU when the Superman plays it correctly.
Aquaman
Disadvantage/Heavy Disadvantage: This character is honestly just stupidly ridiculous so basically, any reason he wins other MUs? Yea, he wins this one for those reasons too. Wins trades, better buttons, can't jump anywhere near him, chip damage, out damages us in the combo department. Oh and his trait. yea, his trait.
Grodd
No. Fucking. Clue. I haven't even played this MU that much let alone lab it.
Harley
Probably Even. Can compete with her fullscreen presence and honestly we beat most of her buttons. Midscreen our wakeups actually kind of fuck with her game plan so it could even be in our advantage.
Bane
Probably advantageous. When he gets the knockdown he face fucks you but who doesn't Bane do that to? Keep him out, space him out, beat his ass. End of discussion.
Robin
Even. Up close he's got buttons to compete and fullscreen he can get in pretty easy if they're playing smart. Both sides get slobberknocked when they knockdown so in that department it's pretty easy. It could be slightly in Robin's favor but idk quite yet.
Fate
Even. We have answers to his shit, he has answers to our shit. Play a really good Fate who knows the MU and you'll know why it's even. (Fate could even win but again, jury is out on that one)
Green Arrow
Disadvantage. He doesn't care about your zoning options. At all. Up close he can compete but yea, he forces you to make your way in much like the Batman vs GA MU.
Darkseid
Even. His zoning isn't too terribly great and we have options against it. Darkseid has some of the worst defensive options in the game outside of D1 and his wakeup which Red Hood abuses. However, Red Hood is free on knockdown which makes it a bit...awkward, for us. They give each other an equal amount of hard time just place patient.
Joker
No clue. See my reasoning behind Grodd.