Octillery evolution would be a fun excuse to do a water/steel. An octopus plated in rusty iron, with a few barnacles here and there, like an old sunken ship's cannon.
A vampire squid (vampyroteuthis infernalis) would make an awesome new water/dark or even water/ghost.
Sawfish is an obvious water/steel.
I also always wanted a parasitic pokemon, like a leech or a tick. It could have a trait that works like an automatic leech seed, stealing a little from the opponent each turn.
A microbe would also be fun, it could be ultra-tiny with only one HP like Shedinja, but most attacks would miss due to its size.
What about a steel/ghost resembling disconnected armor plates? It could have a trait where as soon as it faints, the pokemon to replace it gets a defense boost...as though it "wears" the ghost-armor. There could be a ghostly sword counterpart or something that boosts attack in the same manner.
I've always wanted a giant living brain or eyeball pokemon, as they're my favorite monster types after giant, mutant insects. Would be perfect for ghost/psychic. Maybe a tentacled eyeball pokemon that evolves into a one-eyed, tentacled brain pokemon.
An attack-oriented centipede and defense-oriented millipede would be a neat duo, they could even be freaky elemental pede's, like a fire centipede and rock millipede.
A grass/ghost pumpkin would be an instant favorite for me. Being a Jack-O-lantern, it could be the only grass pokemon to learn fire attacks. Could have a trait that cancels out fire weakness, too.
Course, we could also just have a grass/fire pokemon as well. A jalapeno pepper. Maybe a little humanshape plant, like Roselia, but with a mexican style to it.
A bug/dark cockroach would be another must-have on my team. I'd love a usable pokemon with a humanoid skull face (why must Duskull lose his in evolution?!) and it'd work perfect for a spooky little roach.
A pokemon that changes type every turn would be interesting, maybe with a unique attack that always matches its type. No idea what such a pokemon would look like...maybe a chaotic blob of random stuff, or another abstract machine-like pokemon.
Speaking of which, I would love a pokemon based on the flatwoods monster:
This famous artwork actually doesn't match the eyewitness descriptions of this supposed "alien visitor" (a "towering robot" reported in a NJ forest), but the image is quite popular in Japan. I have seen this monster in tons of videogames, and it would make a great psychic, dark, or ghost pokemon. Psychic/dark?
Speaking of aliens, there are also those tentacled jellyfishlike "martians" in tons of anime/videogames. They would make a fun pokemon as well, another one from outer space.
