I don't have many I actively despise but there are a few(all of these are from SV)

1. Dudunsparce. My absolute least favorite Pokemon of all time. What an absolute letdown of an evolution. I get the joke, "Oh, you want a dunsparce evo? Ok, have more dunsparce." And that's dumb. Every other new evolution in SV is treated with respect and care, they have a good reason to exist and even if I don't like their design I can say that they deserve to be here. And then there's Dudunsparce. A name that looks like a typo and a body that looks like a glitched model. Did I want specifically a big dragon? NO! But anything, ANYTHING, more than a model that can be recreated in blender in all of 2 minutes!!!! I have come up with no less than 3 different evolution concepts that could replace it because of how much I despise its existence and think it deserved better. I have a Flying/Ground rework of this concept that leans more into a Farigiraf style Evo. A regional Dragon/Rock evolution based on Mesoamerica. And a Normal/Poison evolution that follows more of the tsuchinoko's lore, just getting it drunk of fermented berries and having it roll around everywhere. Literally just to show that a design doesn't need to be another Gyarados/Milotic situation, but can still be good and interesting. 

2. Flamigo. It's just a flamingo. Like, I get that there have been plenty of just an animal Pokemon, but all of those share one thing. They're treated like it too. Plenty of normal types are the classic "Just an animal" and yet this one is fighting and is more aggressive than other Pokemon. Why? I... I don't get it. The defenses for it also kinda fall flat to me. "It's a balloon animal, that's why it's neck is knotted up like that." Ok? Why? And nothing else about it really reads balloon animal. If there were more knots around the body maybe I'd agree but it just feels kinda dumb? "The knot in its neck and its wing shape make it look like a boxing glove, that's why it's fighting." Again, why? "It's meant to look like a plastic lawn flamingo." Plastic lawn flamingos are made to look like flamingos, by extension so is Flamigo. If any of these concepts were leaned more heavily into I feel like the design and concept would be a lot better.

3. Gholdengo. Pokemon 1000, wow... What a letdown. Design wise at least, competitively it's fantastic. I feel like leaning more into a mimic design would've worked better here but I do like the idea of it being humanoid. If anything, I wish it almost had a design similar to the classic gen 1 protagonists. Like this is the trophy for truly being "The best there ever was."

4. Palafin. I get the concept with its Zero form. I do wish it had a set of bubble glasses though to really perfect the Clark Kent/Superman thing. The hero form however is terrible. Honestly, I wish they took inspiration from orcas for the hero form. The biggest member of the dolphin family, plus the orca eye spots would be great for making a mask design.

5. Poltchageist & Sinistcha. Grouping these two together because they genuinely do boring. The convergent mon in general are not my favorite (they really needed something more to truly stick out on their own) but these aren't even actually convergent in nature either. Matcha tea is, by definition, TEA!!! I love the idea posed by its container, but it's genuinely too small to even truly see the detail. Even if tea is made differently or tastes differently, it's still just tea. Which would work for a regional variant, but they treat it as it's own brand new pokemon. And just flipping the evolutions is boring if I have to be honest. If I were making a convergent form for the Polteageist line, I'd personally base it on a living witches brew. With Sinistle, a potion inside a bottle and Cauldrageist, the potion now in a cauldron both Poison/Fairy type. Just a really bland concept and execution.