Although it isn't my favorite from a design perspective, I consider Dunsparce my favorite Pokémon. I caught one of these as a kid in Silver Version and raised it expecting it to evolve into Gligar (since they were right next to each other in the Dex and had similarities), but that obviously didn't work out. I even pretended to be a Pokémon Prof. (much like the one who studied Slowpoke and Shellder in the anime), drawing charts and everything documenting their similarities. I sort of grew attached to the squishy lil' guy during that whole process. However, at that point I consided Ho-Oh my favorite since I beat my cousin (whom I had never beaten in a video game before) with it.
Years later on Christmas, before I had gotten the hang of PokéRadar chaining, I decided to check what Pokémon were swarming in Pearl Version. Dunsparce. This reminded me of the time I spent raising one as a kid and left me wondering why I hadn't used one in so long. I was determined to find a Shiny one. And at a fairly low chain and without Repels, find one I did.
That's about the point that Dunsparce became my favorite. I traded "Noko" over to HeartGold as soon as the games came out to replace my starter. He's been in my post-game teams ever since.
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My favorite Pokémon design-wise, however, is Wartortle. It has that tough look, but it's also cute. I love those fuzzy ears, fluffy tail, and that blush. I also really like its Shiny because its shell looks like a big ol' emerald (I've always been fascinated by shiny/metallic green things like emeralds and certain insects). The fact that it can learn my favorite attack, Ice Beam, is another plus!
There are a few Pokémon that I absolutely can't stand, but I suppose Lickilicky would be my bottom pick. I adore Lickitung (probably me second-favorite Pokémon design), but this thing is hideous. It hardly even looks like a lizard anymore, its face looks funny (not in a good way -- it's even worse when its tongue isn't hanging out), the pattern on its bloated torso doesn't look natural at all, and I could've lived without seeing that swirl of flesh on its head. D:
On the plus side, at least Lickitung can utilize Eviolite.