Pokemon that are bigger/smaller than you expected

I suspect that serpentine Pokemon are measured as though they were completely extended upwards, otherwise we wouldn't have things like Ekans being the same size as Venusaur or Dratini being bigger than Charizard. The anime seems to support this (though it does take its own liberties with how big some Pokemon are), as do the size of the walking sprites in HGSS.

So measured as they would normally stand, I'd say Dunsparce would be about 2 feet tall and Serperior around 6 feet.