Question

What are all the Ghost types that learn Thunder?

Answer 1

As of Generation IX:

/nds thunder, ghost:
Annihilape, Arceus-Ghost, Banette, Dragapult, Drakloak, Drifblim, Drifloon, Flutter Mane, Froslass, Gastly, Gengar, Gholdengo, Giratina, Haunter, Lunala, Marowak-Alola, Mimikyu, Misdreavus, Mismagius, Rotom, Shuppet

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Answer 2

Gengar, Misdreavus, Shuppet, Banette, Drifloon, Drifblim, Mismagius, Froslass, all Rotom forms and Giratina are all of the Ghost types that can learn the move Thunder. (I'd recommend using Gengar, it has the best Special Attack and Speed out of all those Pokémon)

Source

Comments

what about haunter ! ?

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Haunter can't learn Thunder for some reason (unless the DB is incorrect), but it can learn Thunderbolt.

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I think drifblim can also learn it

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Yes driftblim can learn it.