-These numbers are assuming Grodd is on his home turf of Gorilla City
Aquaman 4-6 (Possibly 3-7)
Atrocitus 3-7
Bane 4-6
Batman 4-6
Black Adam 4-6
Black Canary 6-4
Blue Beetle 5-5
Braniac 5-5
Captain Cold 6-4
Catwoman 4-6
Cheetah 4-6
Cyborg 6-4
Darkseid 5-5
Deadshot 4-6 (Possibly 3-7)
Dr Fate 5-5
Firestorm 5-5
Flash 4-6
Green Arrow 4-6
Green Lantern 4-6
Harley Quinn 4-6
Joker 4-6
Ivy 5-5
Red Hood 4-6
Robin 5-5
Scarecrow 4-6
Supergirl 4-6
Superman 4-6
Swamp Thing 5-5
Wonder Woman 3-7 (Possibly 4-6)
Losing: 18
Even: 8
Winning: 3
Aquaman is 3-7 or worse. This MU is just fucked up. You cant leap FtD reliably even on predicting it, you cant punish it (you have to ex mb stampede on predict - thats dumb) even if you do manage to get around it and punish there is his trait you cant counter. And the best part about it is that he can choose when to activate it, since your combos restand.
You can punish f2 and b2 on wiff, you cant jump/leap on him, you cant even punish TR reliably etc etc etc. So basically this is about as bad as it gets.
Atrocitus is totally ok on the other hand. Grodd has easy time countering Cat with mb stampede or trait of his own (wheather its MB float or just primal rage), you can outfootsie him due to terrible atrocitus mobility, you can reliably apply leap crossups on him (well , at least sometimes) due to rather bad Anti-air (relatively). you can punish bloodnado very painfully from almost anywhere on screen. I believe this mu is 5-5 or favorable for Grodd.
Batman is broken, but once again Grodd of all people has great answers to bats and also batman has very hard time punishing stampede (safe most of the time), so you can spam it, you can also leap at batman quite well since his AA,while being quite good, doesnt reach behind him, you can leap or primal rage between batarangs making his zoning (and bats) obsolette (which is normally a problem for melee characters in this mu). Finally your d2 is quite good and you can literally poke with it preventing jumps (though you can prevent it via stampede). Finally batman has terrible range of normals allowing you to at least play normally (unlike aquaman there is nothing you have no answer to). So id put it at 4-6 only for reasons of batman being broken overall. In terms of toolset this mu is ok.
Adam is 4-6 just like batman. You have all you need to win, but Adam is broken.
Deadshot is probably 5-5 or advantage for grodd, just because you lose to Foxy doesnt make this mu so bad. In reality Deadshot has no way of stopping Grodd to come in and has terrible defence and bad anti airs once this happens.
Robin is pretty bad MU for grodd as he has so much range you have no solid counterpoke aside of b3(since it kinda leans back between hits) and his smartarangs let him easily contain you. Also due to grodd size he has unblockables on him in the corner (d12-ex divekick if not immediately poked out creates double-crossup that cant be blocked)
Catwoman is very bad for grodd with no solid answer to db3 and great AA from Cat, you literally have to hard-guess your way to victory. Nvm she easily beats 22 with d2 at any point of animation along with other things. Grodd also has some of the worst hitboxes to AA her j2. Possibly 3-7 here
Superman is obnoxious for Grodd as due to his size and backdash every touch from Sups even on midscreen bacially creates a corner-like pressure. As you cant backdash or walk away from f23breath f23breath , leaving no choice but d1 which never nets any proper reward. Needless to say superman neutral and mobliity is better than grodd. The only decent thing in this mu is leap but its not very realible as superman has a lot of freedom to counter it due to his mobility and no way for grodd to really contest his midscreen (i.e its not rare to see sups dash forward reacting to leap and punish your wiff)
I got tired of writing at this point so I'll leave it at that