Like I said, my reasons are really kinda petty.  I just don’t like the change from happy, smiling Koffing to bloated, miserable, lung-cancer-y Weezing.  It actually is quite a creative design, and you could even interpret it as illustrating the accumulating detrimental effects of air pollution (or cigarettes?) on a person’s health, and I can easily understand why other people would like it.  It’s just not my cup of tea, personally.

There is no underground part of a Diglett; a Diglett’s hole is actually a hole in space-time that connects to Giratina’s nightmare dimension.  That’s why you don’t have to be touching solid ground to use a Diglett in battle.

…I’m not sure what you’re asking.  Other than the fact that Dodrio is apparently slower than Doduo (who is described in Crystal, Emerald and Fire Red as running at 60 miles per hour) it all seems perfectly reasonable.

Oh… that’s a tough one.

There are a couple that I sort of have these weird, kind of irrational grudges against, and the biggest one of those is probably Rayquaza, which I dwelt on at some length last year.

I don’t have much of a problem with Rayquaza’s design, or powers, or really with any of the things normal people think about when deciding which Pokémon they like.  When I think about legendary Pokémon, I normally think about how well they fit into the story and how they develop the atmosphere of the world, since that is, in my opinion, what they’re really ‘for’ – they are ‘legendary,’ after all.  Rayquaza irritates me because his involvement in the climax of Emerald version is sheer deus ex machina and utterly robs the player of agency in the resolution of the Hoenn crisis.  You don’t even get much satisfaction out of completing the Sky Pillar (which is much easier than on Ruby and Sapphire) or finding Rayquaza in the first place (since the scene with Wallace in which you figure it out is totally nonsensical).  ‘Rayquaza fixes everything’ is simply not my idea of a well-done climax sequence.

I actually really like Mawile as well.  She’s one of the Pokémon I lump with Farfetch’d, Dunsparce and the like, where they’ve taken a really clever design, made it awful at everything, and then forgotten about it.  Poor Mawile…

Anyway.  I am led to understand that Mawile is probably based on an obscure Japanese monster – a woman with a second mouth growing out of the back of her head.  Game Freak seem to have adapted the idea by combining it with the concept of an animal which uses markings or unusual appendages to appear larger or more threatening than it really is (unlike, say, Girafarig, Mawile doesn’t actually have two mouths; according to the Pokédex the extra ‘jaws’ are really horns).  It’s a very fun, creative design, and I think it’s a shame Mawile had to… y’know… suck so much.  In answer to your question, then, just ignore the big jaws – that’s what she wants you to focus on.

As for why they decided to make her a Steel-type… you know, I honestly have no idea.  Her origins seem to fit with her being a Dark-type, and she’s portrayed consistently as a deceiver.  The Pokédex very insistently describes her jaws/horns as being made of steel, but that seems like it was a later choice to justify the typing, not the reason for it.  Quite aside from that, she has few typical Steel-type powers.  I guess you could interpret it as Mawile deliberately cultivating the appearance of one type when she actually belongs to another, thus continuing the theme of deception and making it more difficult for her enemies to attack her.

What do I think of who?

Heh.  Sorry, couldn’t resist.

Qwilfish is, quite honestly, one of the few Pokémon I have ever just forgotten about completely.  Jim and I were looking through my Pokédex on Diamond a couple of years back and we found this empty spot and just stared at for about ten minutes before admitting we had no idea what the hell was supposed to go there.  I don’t know that this is entirely Qwilfish’s fault.  I think it’s largely because Game Freak have a tendency to hide him.  He doesn’t evolve, he’s too strong to be available early, and too weak to be useful later on, so he kinda winds up being one of those random Easter Egg Pokémon that most people only go looking for because they notice an empty space in the Pokédex and can’t figure out why.

I mean, I know he’s, like, supposedly a really good (if somewhat bizarre) Spiker/Toxic Spiker on a rain team or whatever, but is there really anyone, anyone in the world, who has an empty spot on their team and their very first thought is “Qwilfish would be awesome here”?

The sad thing is that he’s actually based on a comparatively interesting fish; it’s just that Game Freak have fallen into the typical Water-type trap of simply translating a real animal into Pokémon game mechanics and then going no further with it.  I don’t think he’s actually a Pokémon based on a porcupine fish at all; I think he’s legitimately just a porcupine fish.  So I suppose he wins badass points for being usable at all, right?