A parasitoid is any parasite which completes its life cycle by killing its host, a life style wasps have adapted to more than any other form of life, planting their eggs in the bodies of other insects. As gruesome as this is, it's all a part of nature's balance; many plants even deliberately attract these wasps to destroy leaf-eating insects!
Pokétential: please, oh please give us a parasitoid who randomly evolves from other bug pokémon. The look on a trainer's face when a wasp hatches out of his Metapod would be priceless. Its design could even borrow from Alien.
Dangling sticky mucus from its mouth to trap planktonic prey, this amusing denizen of the deep-sea abyss belongs to the same class as the Bobbit worm, but you could never tell from its fat, rounded body. Its lack of reproductive organs implies it's just a larva, but we have yet to find an adult...
Pokétential: could do with goofy eyeballs and a drooling mouth, but while I'd prefer it remain weird and hilarious, I could also see it evolving into something unexpected - a beautifully colorful swimming worm or terrifying, even Cthulhu-like sea monster.
I've decided to spare you trypophobes a photograph of an egg-carrying female...but just this once. These weirdly flattened, fully aquatic frogs are famous for their strange, and to some, highly disturbing reproductive habits, rearing eggs and young in the flesh of the female's back.
Pokétential: some have interpreted Seismitoad as a Pipa, but I don't think it counts without a swarm of offspring living in its back. Like my suggestion for the harvestman, it could continuously generate "substitutes" to shield itself. You know, like any loving mother!
Like the Daphnia or "water fleas" I mentioned earlier, these tiny freshwater flatworms are a staple of high school and college biology labs, where students get to chop them apart and watch every single piece grow into another planarian. Their cartoonish "eyes" are really just light-sensitive spots, but aren't they just adorable?
Pokétential: an unassuming water or normal type with obnoxious regenerative powers, perhaps regaining hit points every turn even without a weather effect or attached item.
This prehistoric relative to the modern elephant seemingly used its extremely long, strangely shaped jaws to strip the bark from trees and even cut off whole branches, an adaptation which no doubt spelled trouble for its predators and rivals as well.
Pokétential: I look at this thing and I see a steel type with an angular, orange-yellow body and a chainsaw-like lower jaw, calling to mind the heavy machinery used to tear down great swathes of forest.
What really needs to be said here? Pumpkins are the universal symbol of the only holiday I officially recognize, and a pretty cool plant with rather prickly, creeping vines and star-shaped yellow flowers.
Pokétential: it's downright criminal we don't already have this celebrated gourd amongst the grass types. It would no doubt be designed with a Jack O' Lantern face (perhaps randomized from a pool of different eyes and mouths?) and a great excuse for grass/fire. An ability resisting "normal" moves could simulate an additional ghost quality.
Like dolphins, Deinonychosaurs are often idolized by people with a flimsy understanding of them, knowing them only as "raptors" thanks to Jurassic Park's contraction of "Velociraptor." In the decades since this inaccurate portrayal, we've learned that these animals were completely covered in feathers, more chicken-like than draconic, and their frightful-looking talons were more likely used for climbing than killing.
Pokétential: fitting if it began as a scaly, lizard-like theropod only to evolve into a flamboyantly feathered fowl. It could still be something like dragon/fighting...happy?
As I've written about here, these amazing microscopic animals have vacuum-like mouths, jaws in their "stomachs," a single leg and (in certain species) can actually incorporate DNA from any other life form into their own chromosomes.
Pokétential: I've suggested several microorganisms by now...wouldn't it be cool if you could collect pokémon that were actually microscopic, but have them enlarged in a laboratory? Not much stranger than bringing fossils back to life, really. This one could boast a unique move which permanently copies the opponent's type or stats, until it's used again!
Though shark-like in appearance, this strange cartilaginous fish is actually an unusual ray, like the mantas and stringrays. Its barbed snout is used to root for prey in sediment as well as a weapon, quickly jabbing at attackers or potential meals.
Pokétential: come on, gamefreak. There's a real fish with a cartoon hedge trimmer for a face, and it wasn't already a water/steel pokémon a decade ago? Yet again though, we make it a sand-swimming ground type, maybe even a rival to my Narwhal suggestion.
"Sea pigs" or scotoplanes are a fairly odd group of sea cucumbers, cousins to the starfish, crinoids and sea urchins. With their tentacle-like "feet," scotoplanes walk along (and consume) the bacterial sludge of the abyssal floor, and are the most abundant animals in this cold, dark environment.
Pokétential: while scotoplanes don't demonstrate the same tactic, sea cucumbers are famous for their ability to spit out their own entrails as a defense mechanism. A sea pig pokémon should totally be explosive.