If Sceptile is added to the list, I believe Lilligant (and arguably, Venomoth) should be included on the list. I have used Lilligant a few times in the past and I definitely think it's a solid high-C, or even a B (as the only thing preventing it from getting more usage are that Roserade and Shaymin are fierce competitors for a spot on teams ). Lilligant can easily set up thanks to Sleep Powder, and it's pretty difficult to stop because it hits ridiculously hard after a boost.
As for Venomoth, it can both fulfill the role of a supporter and a sweeper one, and I think it's on par with most C pokemon.
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