I'll be honest, I think this was the worst pokémon episode I've ever seen. People comparing this to Sun and Moon, this is nothing like Sun and Moon. Sun and Moon had solid and consistent character writing, the characters had motivations and emotions that made sense, were shown, and were consistent for their characters. Even in the comedic filler episodes. This on the other hand, doesn't. There is no motivation set for Go to join the Magikarp competition, he just goes train for it without the episode ever establishing why this thing grabs his interest. Then there's a training montage, and then the event with a one-off rival character to beat. In terms of raw plot, it's similar to say, the Charjabug race episode from Sun and Moon. A competitive event is established, a protagonist decides to join, training montage, event happens and protagonist does well thanks to training. Only difference is, that episode actually established Sophocles' motivation to enter, actually expanded upon the race mechanics with different roles and things that had to be done like changing tires, established a roadblock in the training with Charjabug's initial lack of motivation and struggles to work together with Sophocles, and had challenges happen during the race that Sophocles had to overcome, like how he had to overcome steep inclines in the race by having Charjabug climb and drive across Ash or how he conquered low grip with applying Charjabug's String Shot on the tires. This episode establishes none of that. There are no concrete roadblocks for Go to overcome, there is no motivation established, and nothing happens in the event itself. All the Magikarp do is jump. That's literally all there is to it. No technique, no twists, nothing more than that. This is literally the most barebones way of executing the "train from novice to participate in an event and then do well to show growth" plot ever, the execution is horrible.
Then we get to the results of the competition. Unlike previous episodes that also use this plot format like the episode with the snow sled jumping from Sun and Moon, or the Charjabug race, or Mallow competing in the cooking competition, the results here are absolutely ludicrous. Go's Magikarp literally reaching space doesn't make any sense. Sure, it's a kid's show about magical pets, but even then, there is at least some kind of limit of what is believable within this universe. Lillie didn't become world-class pokémon sled jumping in that episode, Charjabug didn't drive faster than the speed of sound. And it's not even funny. Jokes have to have at least some kind of punchline, at least some element to them that makes you think "okay, that was weird and unexpected, but it also somehow makes a bit of sense now that I think about it". Like how Kiawe blowing up the living room in the Z-pose game in the sleepover has underlying that it makes sense for his overly competitive character to go overboard, especially when Inferno Overdrive comes up. This is weird and out there, but there is no underlying sense to Magikarp reaching space. There's no double entendre either, there's nothing that ties Magikarp or Go to space. And if you think Bewear was also insane; it was, but it was established from the beginning to have insane superpowers that they slowly built up more and more. It made sense in a way because it was Bewear, and Bewear was just Bewear. This Magikarp doesn't have any of that established build-up, it just comes out of nowhere.
To come back to character writing, Go's response to his pokémon literally ending up in space. He doesn't care. He spends an entire training montage with this fish, but when he literally loses his pokémon there is nothing to show that he cares. Nothing at all. Not even a single shot showing any kind of grief or "oh no is Magikarp going to be okay" or "oh no I lost Magikarp". The episode doesn't care, the storyboard doesn't care, nobody cares. Go gets disqualified, and without even doing the bare minimum, like trying to look for a way to save his Magikarp and reunite with it, he just goes on to his next adventure. In the Raboot in Hoenn episode and the episode with the missing food at the lab Go actually displayed some level of concern for his troubled pokémon and did his best. He was awful at figuring out what was wrong with his pokémon, but at least he tried, and I was hoping that at least they were trying to establish some kind of empathy and character growth with him, but then this episode comes and all that is just squandered and destroyed when he doesn't even display the slightest bit of care when his own pokémon that he spent an entire training montage on in this very episode literally ends up in space and likely lost forever if he doesn't act. It just paints his character as a horrible person, it's even beyond how Misty treated Psyduck back in the days of OS. It's on the level of how Charmander's original trainer back in OS abandoned it in the rain. In other words, it's on the level of how villains treat their pokémon when the writing has to establish those villains as evil. The only reason why it's not immediately apparent to the audience how horrible this is is that Magikarp doesn't have a personality or display any kind of emotion, it might as well be a plushie with a jumping mechanism inside. Magikarp isn't presented as something with consciousness or emotions at all.
And then there's the second half of the episode, completely disjointed from the first half. It's weird, most of it is just the characters playing hot potato with the Shellder, and that's it. There's no motivation to be found, no character, no twists, it's just a repetitive gag that goes on for way too long when it's not even that funny after the first time. If they want to keep the joke going, at least add unique twists to it instead of just repeating the same gag over and over again, it just drags.
Altogether, this episode was horrible. It rushed from event to event without establishing characters, didn't even consider the implications that the actions of the characters have for what those actions tell about the characters, made absolutely no sense, had little to no comedic moments that were genuinely funny or clever, only did the most barebones approach to this kind of plot without any kind of obstacles for the protagonists to deal with, and actively proceeded to annihilate Go's potential as a likable character by having him abandon his own pokémon in the vacuum of space without care. At least Damien's Charmander could have feasibly walked to a pokémon centre.