The Opah Fish exists to make you uncomfortable. Serge is in the middle of a Hot Date when he’s suddenly swept into an alternate dimension by the fortuitous convergence of temporal instability, traumatic panther-related flashbacks, and a fancy CG cutscene (Chrono Cross’s protagonist “crosses” between 2 dimensions just as Chrono Trigger’s protagonist “triggered” through time. It just. MAKES. SENSE.) TALK about AWKWARD. “Another World” is exactly the same except that, in it, Serge died ten years ago, which apparently changes a heck of a lot of stuff. The presence of Opah Fish is one of the first differences you’ll notice.
Whereas the beach beasts of Serge’s home world were cute li’l scamps with great smiles, the Opah Fish is a hideous monstrosity. It looks sort of like the weird floating fever dream sperm version of that one Digimon. Nightmarish, truly. It also has a red innate and shoots fireballs, which is not something a fish should do. Speaking of which, did I mention that it floats? There is no water involved in the equation, it literally swims through the air. I’d even say, with these things around, water is probably the only place you’ll be safe. They’re unpleasant, but as a narrative device they’re useful in letting you know you’re not in JRPG Kansas anymore.
Passing through the alternate world’s Lizard Rock, you’ll run into a group of Opah Fish swimming in a circuit around a coral reef. You’ve got to run their path to get out of the area, and they’re faster than you, so inevitably you’ll wind up getting caught by 1 or 2 of them. It’s annoying, but you have to fight and then run and then fight and then run. In other words, you have to fight the Opah Gang ‘Nam Style.