Along with Water-types, Grass-types might be the most recognizable Pokémon in the franchise. There's no way to misidentify them or confuse them for another type. They almost always come in shades of green or brown, with some sort of plant or flower motif in their bodies.
However, some Grass-types stand out because of their unique and rather unfortunate designs. Calling them ugly might be a tad cruel, but there's no other way to explain it. Indeed, these Pokémon are so unappealing that many Trainers would probably avoid them if they ever saw them roaming in the wild.
Carnivine
Introduced in Generation IV, Carnivine is a pure Grass-type without any pre-evolution or evolutions. It is mostly a forgettable inhabitant of the Sinnoh region that doesn't stand out in any way. It has below-average stats, save for an excellent Physical attack, but pales in comparison to the region's other Grass-types.
With its humongous mouth and ridiculous smile, Carnivine is more dumb-looking than ugly. It also has an equally goofy attitude that makes it slightly more memorable. However, when compared to some of the other Sinnoh Grass-types, it's clear that Carnivine got the short end of the stick in the looks department.
Exeggutor
Exeggutor might be part of the original 150, but it is far from being one of the most iconic Pokémon from Generation I. Exeggutor's dual Grass/Psychic-type leaves it with a whopping seven weaknesses, including a four-times vulnerability to Bug, making it a tricky Pokémon to use.
In terms of design, Exeggutor isn't so lucky either. Its three heads look slightly disturbing, and its lack of hands makes it look like a half-finished creature. Exeggutor's Alolan form isn't much better either, because its absurdly long neck messes with the already weird proportions, creating a Pokémon that's very unpleasant on the eyes.
Parasect
In the pantheon of Pokémon no one thinks of, Parasect holds a place of honor. It's been part of the franchise since day one, and still, no one seems to ever show it any love. A dual Grass/Bug-type, Parasect has pitiful stats and two four-times weaknesses, making it an absolute nightmare to use.
Parasect's lore is also somewhat tragic. The parasitic mushroom on its back took complete control of its body, effectively turning the insect into a zombie. Design-wise, it lives up to this sinister concept, with a pair of blank eyes that effectively convey the lack of life behind them.
Trevenant
Many Pokémon have scary designs, but few are as terrifying as Trevenant. This dual Ghost/Grass Pokémon has some underwhelming stats, which might not make it the best choice for a Kalos playthrough. However, it also has two immunities, so experienced players could make it work.
However, those Trainers looking for aesthetically pleasing Pokémon should stay away from Trevenant. It is the Pokémon version of a cyclops, and its hollow body makes it extra creepy. To be fair, Trevenant is a ghost and therefore meant to be terrifying. However, its lack of features beyond that red and menacing eye make it far too ugly, even for a specter.
Cradily
Fossil Pokémon can be pretty strong, but their strength comes at the expense of their looks. The best example is Cradily and its pre-evolution, Lileep. These dual Rock/Grass-type Pokémon are tanks that can be valuable team members when appropriately used.
However, they are both hideous, especially Cradily. Its two sinister glowing eyes would be enough to make place it among the most unappealing Pokémon ever. However, its extendable neck, which can reach up to three times its usual length, cements its place in the hall of fame of ugliness.
Victreebel
Victrebeel wears its inspiration on its sleeve, borrowing plenty from carnivorous pitcher plants. As one of the first-ever Grass/Poison-types, Victrebeel has excellent Physical and Special Attack but below-average everything else, making it a capable but tricky option in battle.
Victrebeel has another thing going against it, unfortunately, and that's its horrible appearance. Victrebel's humongous trap is unappealing enough, but the bizarre placement of its eyes and its oddly shaped body do it no favors. To make it worse, Victrebeel has one of the worst Pokémon cries in the franchise, a screeching, banshee-like wail that makes the skin crawl.
Amoonguss
The Unova region has several underrated Pokémon, but Amoonguss isn't one of them. In fact, fans can't wait to forget about this unfortunate mushroom Pokémon. Amoonguss is one of the many Grass/Poison-types in the franchise and has absolutely nothing to make it stand out among the crowd, except for its pitiful Speed stat that stands as one of the worst in Pokémon.
It doesn't help that Amoonguss is also exceptionally ugly. Its Pokéball-shaped head makes it more obnoxious than quirky, and its bizarrely swollen mouth gives it a somewhat disturbing look. Amoonguss isn't even cute in terms of personality, as the anime showed it to be serious to the point of stoicism.
Abomasnow
Poor Abomasnow carries the burden of having one of the single worst type combinations in the entire franchise. Grass and Ice are frail enough on their own, but together they become even worse with a staggering seven vulnerabilities, including a quad weakness to the common Fire-type. Above-average stats can't make up for an awful Speed Stat, so Abomasnow remained an inconvenient choice until Gen VI gave it a Mega Evolution.
It's not all terrible, because Abomasnow appropriately portrays its inspiration, the legendary abominable snowman. However, "fearsome" often translates into "ugly" in terms of design, which is the case here. Indeed, Abomasnow is a terrifying golem, and anyone would probably have a heart attack if they ever encountered it amidst a snowstorm.
Tangrowth
Generation IV introduced multiple evolutions to previously single-stage Pokémon. For the cute but otherwise forgettable Tangela, they settled for the decidedly-not-cute and far more memorable Tangrowth. One of the most powerful pure Grass-type Pokémon in the games, Tangrowth boasts an exceptional 535 Base Stat, boosted by its massive Physical Defense and Special Attack.
Unlike other ugly Grass-types, Tangrowth is excellent in battle, which is great because it is one unattractive Pokémon. Tangela is cute in a weird sort of way, but Tangrowth is just plain busted. It's also very goofy-looking and seems slow to the point of exasperation. But hey, at least it's strong!
Simisage
It wouldn't be an understatement to say the Unova monkeys are the most unattractive Pokémon in the franchise. Fans have near-universal contempt for these three apes, considering them borderline ridiculous. It's a shame because Simisage is a decent Pokémon, thanks mainly to an admirable Speed Stat.
However, in terms of design, Simisage does fall short. Its overly humanoid appearance already makes it controversial enough, and that absolutely ridiculous pompadour doesn't make things any better. It might not be as hideous as its Water-type sibling, the unbearable Simipour, but Simisage is no prize either.