Bacteria are a sadly neglected kingdom in popular culture, despite the fact that they're quite literally everywhere and essentially running our planet behind the scenes. Most are harmless or beneficial, but some of them generate toxins that can make us quite sick.
Pokétential: a two staged pure poison type in the tradition of Grimer, Koffing, Gulpin and Trubbish, it could evolve from a single fuzzy little cell to a whole floating cloud of enlarged bacteria acting as one creature, varying in form.
ISOPOD:
Known as woodlice, sowbugs, pillbugs and roly-polies on the surface world, these crustaceans are far more diverse and often far larger in the sea, including the "tongue biter" already featured and the incredible Bathynomus giganteus, shown here. These ghost-white sea lice can exceed a foot in length, scavenging dead or dying animals from the mucky floor of the deep sea abyss.
Pokétential: instead of bug/water, let's just put these giants in caves as pure bug types, perhaps wih humanoid skull-like faces, which is already a subtle impression I get from the real thing.
JANTHINA:
Also called the violet sea-snail, this amazing gastropod spends its adult life hanging upside-down from a floating raft of hardened bubbles, traveling with the current and feeding - much like Glaucus on the previous page - entirely on other floating animals like the Portuguese Man O' War. Poor Tentacool can't catch a break!
Pokétential: I know I already suggested this with cone snails...but besides an obvious water type, I'm seeing another candidate for a Magcargo evolution, hanging from a blimp-like mass of lava bubbles. Come on! He needs it!
KOMODO DRAGON:
The largest lizard alive today, this powerful meat-eater enjoys both rotting, filthy carrion and living prey, subduing the latter with a possible venom and the toxic bacteria swarming in its filthy slobber!
Pokétential: do I need to say poison/dragon? With nasty-looking slime dribbling from a toothy maw, I could finally find myself really loving a dragon type.
LARVACEAN:
I've written about these multiple times, and they never cease to amaze me. These extremely tiny tunicates somehow generate a complex mobile "house" of mucus that we see here. The animal may be only an inch long, but its slime-shipe can be several feet across. The whole structure is driven by its tiny tail, and gathers planktonic into an internal filtering structure.
Pokétential: a huge, gelatinous "submarine" or even frightening slime-monster created and controlled by the tiny creature at its core.
LATTICE STINKHORN:
The stinkhorns are a group of fungi named for their corpse-like odor, many species even mimicking the color and texture of rotten meat. Flies attracted by this stench help to spread the fungus as they feed on a black slime loaded with spores. Stinkhorns come in many, many shapes, but these brain-like structures are one of the most striking.
Pokétential: a ghoulish grass/poison type, with slimy black tentacles emerging from its cagelike body.
LEECH:
One of my favorite animals since childhood (gee, you think?) these earthworm relatives are most famous as bloodsuckers, though the majority of species are scavengers or even predators. Long ago, doctors used them for the obsolete practice of bloodletting, but we now put them to slightly different, nonetheless amazing medical use.
Pokétential: to differentiate from the Lamprey pokémon Eelektross, this could be a slug-like water type with unique healing moves; perhaps able to drain a little health from the opponent and give it to a team member?
LIONFISH:
The regal fins of this colorful predator are a warning to larger creatures that their fin rays pack a lethally venomous sting. They feed on just about anything they can suck into their large mouths, and have been observed blowing water jets at prey to cause confusion.
Pokétential: It's not the last time I'm going to suggest this, but let's go with water/fire, "stinging" opponents with heat rather than poison. Its ability could negate water's resistances to fire moves!
MANTIS SHRIMP:
Stomatopods are easily one of nature's most formidable crustaceans, armed with either "spearing" or "smashing" appendages capable of striking with the force of a gunshot; even generating a sonic burst which further injures prey. Their bulging eyes are a contender for the most advanced in nature, able to perceive colors unknown to the human mind.
Pokétential: excellent candidates for a complete water/bug lineage, a "spearer" form could have higher special attack, while a "smasher" would focus on physical damage. A unique signature move could automatically strike first.
MARINE IGUANA:
The only amphibious lizards adapted to salt water, these spike-topped creatures are excellent swimmers and feed exclusively on algae, diving for short periods to graze on slimy, submerged rocks.
Pokétential: echoing my thoughts on the basilisk, a marine iguana is prime material for a water-type "starter" at the beginning of the game, all of which are traditionally patterned after amphibious vertebrates. Of course, we could also be looking at a fire/rock lizard who dives straight into volcanoes.