Alright, let's look at this from a region-by-region basis.
>Kanto: Koffing
At least Magikarp can evolve into Gyarados. Here? You're a stinky gasball that only gets stinkier upon evolution.
Johto: Unown
I was tempted to say Miltank, but at least then you can produce delicious milk for society and would probably be popular with the ladies. If you're a guy, getting gender bent might not be fun, though. Being an Unown, however? One move that might not even be a good type, you're stuck in some old ruins where barely anyone treads, and lord forbid if that Glury autist finds you...
>Hoenn - Spoink
Aside from being a pig, you're also forced to bounce forever or die from your heart stopping.
>Sinnoh - Stunky
I mean, do I even need to explain? You're a walking fart joke with a literal assface.
>Unova - Garbodor
Again, do I need to explain?
>Kalos - Goomy
You're a weak little slug dragon, and if you evolve you'll go blind. Evolve again and you're a fat fuck.
>Alola - Pyukumuku
You're a sea cucumber that has a literal anus mouth, barely any offensive capabilities, and spits out your own guts. Not to mention The youngster copypasta
>Galar - Dracozolt
You're a genetic abomination with a dumptruck ass. Need I say more?
>(Gen 9 region) - Lechonk
Maybe it's too early to say, but so far Lechonk because pig.
