Damn,Pokemon fights are a real pain to define as they have acess to their whole move pool/abilities and said things still have their own RNG.
So Groudon has a minor ap advantage (1.333...x Garou's AP), some of his moves (mud shot, scary face, earth power) can inflict stat reduction by levels(wich i'm not sure the exact % they represent) altough earthquake is likely the best one to spam since it deals AOE and has high accuracy. he can also buff himself with bulk-up (att and def)
Pikachu would be the deciding factor here, as he seemingly has stuff like sleep manip stat induction, statistic reduction moves and buff, but since he's berserk i see him focusing on DPS with offensive moves and occasionaly buffing himself rather than support wich is a bad thing for this fight. His static ability however can screw Garou if it happens at a bad time, not to mention
Garou has extraordinary technical skill who allows him to dodge Saitama through analytic prediction(Garou even stating he wouldn't be able to dodge the latter with just his movement speed + reflexes alone) WSRF who can deflect most non AOE/ non swift moves, (although stat reductions like scary face still remain), and fissure(BFR) has pretty low accuracy. got turned into charcoal by Orochi in a weaker form wich makes me believe burn status likely won't work and has mid-low regen, which allows him to insta-regen from stuff like getting his arms vaporized by serious moves and getting a big hole in his face a+ Imortality type-2 in case something important gets broken.
Very close to an incloncusive for me, Garou can dodge and repel most direct attacks like electricity and beams, and since the AP difference isn't very big, he can tank earthquakes from a non-amped Groudon and pikachu just fine with his regen+immortality,plus his adaptation lets him grow things like wings, another problem for groudon. I will also state it's in character for Garou to try attacking eyes with his claws. Thing is, if Groudon decides to spam self-amp, the battle will start to become harder and harder for Garou, if he hasn't adapted to paralysis yet, there's a fairly high chance he gets prlzed hitting pikachu and then gets hit by a monstrous blow from groudon.
Tldrl: i see Groudon and pikachu taking this if they spam stat amp early on and getting Garou paralyzed at a bad time, i see Garou taking this if they don't do that soon and the battle drags too long.
