Yes, I do picture Oddish as a dark type. Especially it's older versions. Also, if you read it's pokedex entry, Oddish is nocturnal and only comes out at night to spread it's seeds. In the original gen 1 games, the spites depicted it in a black color. Also, Gloom learns the move moonlight. There are several reasons it would make a good dark type.
Staryu and Starmie for the same reasons. They come out at night, they are mysterious (sort of like alient type creatures) Yes they are starfish, that's why I see them as water/dark.
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