FF7 Rebirth's Golden Saucer has a wealth of minigames to explore, but some are harder than others. One of them is definitely the Musclehead Colosseum, which can be harder or not depending on who you bring into the fight.
FF7 Rebirth: How to Win Gold Saucer Combat Challenges (Musclehead Colosseum)
One thing to keep in mind is that you are not obligated to do any of these colosseum fights now. You can simply push the main story forward and do them with someone else later in the game. In fact, I highly recommend doing this if you are struggling.
I’m going to be Cloud-centric with my advice for the first two challenges. After all, I don’t know for sure what partner you’ll have with you on your first visit, and this may be a challenge you want to prove to yourself you can do at this point—and that’s okay!
The third and fourth challenges are 11 levels above the first two. That's your cue to come back later.
