Username: Umbr30n
Partner Pokemon: Rayquaza!
Reason for joining: A few of my favourite Pokémon are serpentine. These are Serperior, Rayquaza and Arbok. I mean, snakes are cool, so I know I should've joined some point.
Answer the current topic: IMO the only problem with two headed snakes is that they won't be that original either. With two headed snakes appearing in other franchises (Viva Pinata and whatever) it's still not that much more original than normal snakes. Besides, if I'm correct no franchise has ever created a three-headed snake (I am not joking, I AM SERIOUS) so this might be a good opportunity for an extra original snake to be made. I do know there may be a few flaws.
As for some snakes being Dark-Type, I think this is quite a good idea. Maybe, just maybe, if there will be a Dark-Type snake, it will be paired with Poison. Yeah I know, Poison is a common Type for snakes, but it really describes its personality and traits. Also, it could do a bit more damage to a variety of Types.