What ingame trainers in Pokemon Blue and Sun specialize in one type?

Question

This list can't include Gym Leaders, Island Kahunas, or people in the Elite Four.

Comments

Pokemon Blue? Do you mean Pokemon Sun and Moon?

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In Blue, I'm pretty sure gym leaders and elite fours are the only NOTABLE trainers that specialize in one type. In Sun, there are trial captains, Sycamore's assistants, Plumeria and Guzma, Faba, Moylane (needs spell check), and Ryuki, along with lots of less notable trainers.

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Not a full answer, but http://bulbapedia.bulbagarden.net/wiki/Type_expert

Answer 1

I'm going to list trainer classes and not specific trainers, as specific trainers sometimes only have a certain type because they have one Pokemon or simply because coincidence.

Pokemon Red and Blue:
Bikers specialize in mostly Poison type Pokemon. The exception being one Biker having two Voltorbs.
Bird Keepers specialize in Flying type Pokemon.
Black Belts specialize in Fighting type Pokemon.
Bug Catchers specialize in Bug type Pokemon.
Burglars specialize in Fire type Pokemon.
Channelers specialize in Ghost type Pokemon.
Cue Balls specialize in mostly Fighting type Pokemon. The exception being one of them having two Tentacools and a Tentacruel.
Engineers specialize in Electric type Pokemon.
Fishermen specialize in Water type Pokemon.
Hikers specialize in mostly Rock type Pokemon. The exceptions are a few of them having Machops.
Jugglers specialize in Psychic type Pokemon.
Psychics specialize in Psychic type Pokemon.
Rockers specialize in Electric type Pokemon.
Swimmers specialize in Water type Pokemon.

Pokemon Sun and Moon:
Black Belts specialize in Fighting type Pokemon.
Fishermen specialize in Water type Pokemon.
Swimmers specialize in Water type Pokemon.
Janitors specialize in Poison type Pokemon.
Molayne specializes in Steel type Pokemon.
Faba specializes in Psychic type Pokemon.
Ilima specializes in Normal type Pokemon.
Mallow specializes in Grass type Pokemon.
Acerola specializes in Ghost type Pokemon.
Kiawe specializes in Fire type Pokemon.
Sophocles specializes in Electric type Pokemon.
Lana specializes in Water type Pokemon.
Grimsley specializes in Dark type Pokemon.
Ryuki specializes in Dragon type Pokemon.
Sina specializes in Ice type Pokemon. However, when battling her in the Battle Tree, she only has three Ice types out of her seven Pokemon.
Dexio specializes in Psychic type Pokemon. However, when battling him in the Battle Tree, he only has two Psychic types out of his seven Pokemon.
Plumeria specializes in Poison type Pokemon. However, when battling her in the Battle Tree, she has a Lurantis.
Guzma specializes in Bug type Pokemon. However, when battling him in the Battle Tree, the only Bug type Pokemon he uses are Pinsir and Golisiopod. The other five Pokemon he uses are either Poison or Dark type.

Source

Comments

You forgot Moylane, Sina, Dexio, all the trial captains, Faba, and Ryuki. (and Giovanni was a ground specialist when he wasn't a gym leader)

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Whoops! Thanks for mentioning those. I totally forgot that Trial Captains weren't the same things as Kahunas. As for Giovanni, I don't think I'm going to add him, as only three out of the seven Pokemon he used when he wasn't fought as a Gym Leader were Ground type.