In Gen 2's elite-four, the dark type elite uses a vileplume, though it's not a dark type. How come?

Question

So, one of the elite four, if I did not made a mistake, uses dark-types, but she has a gengar and a vileplume. For gengar, I think it's reasonable to have because he is part ghost. But a vileplume?
Could anyone explain this?
Thanks.

Answer 1

Well, to be fair, there weren't too many Dark types. So GameFreak had to resort to using Poison types as well.

Comments

Thanks. Sounds like a good reason.

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Karen does say at the end she just likes to use her favourites. In HGSS, she still had a Vileplume.