Thanks~! :) But yeh in
Paper Mario The Thousand Year Door there are actually three dragons- Hooktail (the one you posted), Gloomtail and Bonetail. XD Gloomtail is Hooktail's older brother and is encountered towards the end of the game (whilst Hooktail is a boss fairly early in the game~).
Anyway Gloomtail'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.