Hitmonchan. There are Pokemon that are basically deities, with powers to control every element, able to use psychic power to manipulate your thoughts, and here we got bro that's just like square up. I respect him. Got some literal legendary beast from time immemorial, worshipped as a god in some cultures, able to turn you to ash in single movement, and Hitmonchan is just like let's fucking duke it out.
Fighting type for life. I ain't gotta think about shit let's just throw hands. Coincidentally, this is also why I always choose warriors/barbarians/melee types in any game or campaign.
Breloom because Spore and Focus Punch is a good move combo, plus Leech Seed is always awesome.
Aegislash because Steel/Ghost is an interesting type with lots of resistances.
Alolan Dugtrio because its hair is gorgeous.
Blastoise! Idk why exactly, he's just a big-fun-boi with silly water cannons and he rarely gets featured in anything, so it's always exciting to find merch or w/e with him on there.
My sad medusa child Mareanie. It's such a fun body plan compared to your common cartoon starfish, and also I'm a disgusting stall lover so Toxapex is a natural fit. Pick any poison type really, and I probably love it.
Honorable mention to Parasect and Mew for being my original faves.
Let me tell you about the Pikachu evolution line, then you'll know three Pokémon!
Pikachu evolves from Pichu:
And Pikachu itself can evolve into Raichu (though Ash's Pikachu refused to evolve when given that option):
The Pokémon world has different regions, and some Pokémon look different if they evolve in a particular region. This is Alolan Raichu, the form that Raichu takes if it evolved in the Alola region:
Pichu actually was added later than Pikachu and Raichu, the very first games (Generation 1) only had Pikachu and Raichu, then Generation 2 added Pichu
Hisuin Decidueye is seeing some usage in VGC if you play that atm. It's kinda workable in trick room and has a really good signature move. It's speed stat is so bad though, not slow enough to always be good in trick room, not fast enough to always be good under tailwind
Hoothoot is perfect and I love them, Noctowl is great too like Decidueye I wish they were more viable for online but oh well. They'll make a buff owl Pokemon one day