Stantler doesn't look bad to me, but it's easy to see why it does: the beak-like nose and face structure in general.
As for Bruxish, good god does that thing look gross. It's the garish colours and especially the human-like lips and teeth, as opposed to even just slightly more fishlike ones like Goldeen. It's like those moments in a disney animation when a human character turns into an animal but you can see the human's traits and design come through... except that human is a 50 year old celebrity who was a hasbeen even when the 80's workout tape they came from was produced.
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Generally, for me, I can appreciate any Pokemon design that I understand why it's made like that. Though I don't mind Togepi, Vullaby makes a lot more sense to me, as it's clearly based on that image of baby birds hatching and squawking while still in the egg. Mandibuzz's "bone diaper" is clearly meant to be it's nest.
Incineroar I feel is a design maligned more because of other preceding fire starters than Incineroar himself. Even
@Don't @ Me 's response has a hint of that. And if having the inspiration of Wukong is enough to excuse Infernape, then
@Don't @ Me might be surprised to learn that the wrestling-themed incineroar is based on Tiger Mask, a comic book character evolved into a wrestler persona that's lived from 1968 to today.
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He's also likely the inspiration behind Kemono Michi's mc wrestler and even has a reference character in ace attorney. And probably many others too.
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Just because you don't know the reference doesn't mean that they're not making one,
@Don't @ Me
If we're talking about bad designs, though, can we talk about the time that, rather than any sort of subtle version or reference, they just straight up gave Toxel a diaper?
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I mean come on. You have rockstar-themed evolved forms for a Pokemon and their pre-evo is a literal pantshitter? Not anything cooler or anything thematic? Maybe they could have made it some pre-evolution before a professional musician, like an amateur musician or a drummer. Nope, instead we get the baby in it's most literal form yet.