Thanks for bringing this up Oglemi!
As an adjective etc, I'd favor 'badly poisoned' For example:
- A badly poisoned Pokemon is an easy prey for Torment Heatran
As a noun / present tense, Toxic poison sounds better I think :d
- Blissey hates Toxic poison more than a burn.
Bad poison and toxic poison seem as if 'bad' and 'toxic' are adjectives to the poison itself >.> Also might want to note that if regular poison and Toxic poison are used collectively, simply poison should do instead of stating both types.