Arena challenges 3 through 5. All of the challenges for tier 3 are against bat monsters. Numerous,
poisonous, bat monsters. Tier 4 are beasts with massive armor, though little health beneath it. The first fight of tier 5 was large, tough beasts(that were also poisonous), and the second fight was unexpectedly against soldiers of Thélème. The last was one of the local gods. Surprisingly, that last one was actually easy, especially since I nearly smashed my computer in rage fighting a different species of local god in Vasco's personal quest.
My companions are... dumb. There's no way to command them, so they do their dumb thing. Most of the time, they ignore enemies hit with Stasis, but in the arena that part of their brain stops working. The reason this is bad is that one of the upgrades for Stasis is that is burns their armor away while they're frozen. It also, obviously, pulls an enemy out of the fight so you can focus on another enemy. It's actually one of the most useful abilities in the game by far. Some enemies resist, leaving them only frozen for one second, but that's still very useful.
So, after all the fights, watching my companions die stupidly, then myself die because I'm outnumbered, I finally beat the arena sidequest. You only get paid
once the entire quest despite the multiple stages of fights, and it's armor I can't even friggin' use because I have nowhere near the stat requirements.