Just wanna muse about prof. tangrowth and slowking for a second. (Pokopia spoilers!!! I haven't played the game, but I have read a lot about it and my AU for these characters involves major plot points from it. Don't read this if you're concerned about being spoiled!!)
I imagine that they meet as a tangela and a slowpoke, respectively, before the events of Pokopia take place. Tangela's trainer is a pokemon professor, but slowpoke is wild. Both live on Fire Island.
While Tangela's human companion is working on his research, he allows his pokemon to wander on their own. Naturally curious, Tangela spends a lot of time both in the lab and outside of it, observing the natural world and using the professor's research texts to understand his discoveries. The lab is located on an atoll that surrounds the volcano, a dense jungle that is almost completely separated from the main island. Tangela wants to explore the main island, but the water is too deep for him to cross safely.
One day while exploring, he discovers an area that seems more shallow than the rest. He decides to try crossing, but the tide comes in and strands him on a sand bar. Afraid and alone, he cries out for help, and his cries are heard by a slowpoke fishing nearby.
Slowpoke doesn't possess the same intellect as Tangela, but he knows a distressed pokemon when he sees one. He swims over and ferrys Tangela back to the jungle side of the island. In exchange for helping him, Tangela gives Slowpoke a cookie he'd been saving in his tangle of vines. Slowpoke is delighted; he's never tasted human-made food before. The two new friends wave goodbye.
The next day, Tangela returns to the shallow area once again, only to find Slowpoke already there, fishing as he was the day before. Tangela gives him another cookie, and Slowpoke ferrys him to the main island for the first time.
The two pokemon spend most of their days this way, exploring together, making discoveries about the island and bringing back all kinds of trinkets and material samples for the professor. It's slow progress, but Tangela even manages to teach Slowpoke how to read basic words. Despite that he could, the professor doesn't try to catch Slowpoke, respecting that he's dedicated to the island and wants to remain free. He and his tribe have a shrine to protect, after all.
One day while exploring, Tangela finds a king's rock half buried in a stream. Not knowing what it's for, Tangela playfully places it on Slowpoke's head, calling him the king of Fire Island. No sooner has he done this, of course, than Slowpoke is enveloped in a powerful glowing aura -- and emerges a Slowking! Tangela is awestruck by his friend's new visage and power, but neither of them have time to bask in the glow of this event; at just that moment, while both are standing at the foot of the volcano, it erupts.
Neither Tangela nor Slowking are very fast pokemon, but having just evolved, Slowking is the faster of the two. He scoops up Tangela and races back toward the professor's lab, barely making it in time. As the lava encroaches, the professor captures both frantic pokemon and places them safely in a special virtual box -- where they remain for many, many years.
When Tangela emerges, the world is completely different. It's still Fire Island... but the volcano has sunken. All that remains is the atoll. Off in the distance, the remaining islands of the Orange Archipelago are shorter than he remembers. He catches his reflection in a puddle and realizes that he's changed, too -- he's a Tangrowth now! He can't wait to tell Slowking, but... Wait... Where is Slowking? As a matter of fact, where is... anyone?
He circles the lagoon where the volcano once stood, looking for any signs of life. It heartens him to find some here and there -- Pachirisus scurrying and Hoothoots cooing in the trees, but... where are the Slowpokes? Where is his friend?
By the time he makes it back to the lab, night has fallen. He huddles next to the PC that he'd emerged from only a couple days prior, wrapping his vines around it. It's just a computer, but considering it had saved his life, it's the closest thing he has to a friend at the moment. As he's about to fall asleep, the screen flickers to life, startling him. An image of a pokeball emerges, and then to his shock, falls through the screen into his lap and immediately emits a blinding shower of light. When he opens his eyes again, he just can't believe it; it's Slowking! He ensnares his friend in a desperate hug, making him laugh and cough as he squirms against the mess of vines.
Now reunited, the two friends embark on a journey to discover what happened to their world and how to help the displaced pokemon who still reside there. Together, they pick up the pieces of their past and construct a better future for not just themselves, but for all pokemon.