Butterfree
Gen 1 it didn’t do a whole lot, it had all the early status effects but not much else.
Fire red and leaf green they added abilities, and gave it some psychic moves, so it became the best status effect inflicter who could then still do something after
Was pretty neutral about Crobat until I decided to relieve frustration about Zubat encounters by catching one myself. Raised it and befriended it, got a Crobat, and found it very useful.
Also, it’s really funny how even when these guys are delighted, they still have that huge frown on their face.
Azumarill. The Huge Power ability paired with Belly Drum makes it one of the best SV Terra Raid Pokémon.
It’s also a Great League staple in Pokémon Go
Cottonee & Whimsicott. I ended up using one in a Nuzlocke, and it was clutch. Prankster is an incredibly useful ability.
Sableye. Small bedazzled annoyance. But in PoGo they hit fast. Sure they max out at Great League CP and a shadow one is going to require almost 300 XL candy that you will need to walk forever for but oh my is it nice.
venasaur for me, as a kid i was a charizard fan (mostly because ash’s charizard) and so used to only pick it. But about 2-3 years ago, i made a soft rule to don’t repeat pokemon between runs, and this time, for radical red i took venasaur, and genuinely started appreciating it