Anyway Hooktail's, poison-based attacks are fairly strong. His Megabreath is the third strongest move in the game, according to the Super Mario Wiki.
In the Pokemon world a Poison / Dragon type would probably have decent offensive stats from both sides of attack. Like some of the other offensive-inclined Poison-types, I guess it would have mediocre defences. I'd like to see it as the next Pseudo Legendary (600 base stat total, three stage evolution line, etc). :3 As for its concept/origin I have no clue XD.
Oh yeah, I'm sure they will have another Dragon Pseudo Legendary when 6 Generation comes along. They seem to keep bringing in more and more. I'd be interesting to see how much newly form 'Poison' Pokemon they can bring in.
I think they should bring in more spiders (I know..yuck). I can only think of two right off the top of my head, but with all these poisonous spiders out there, I'm a bit disappointed. Galvantula who isn't even Poison type, and we have the lone Poisonous Spider, Ariados.