>>32353528Fungi are genetically closer to animals than they are to plants. Still, Grass works fine for mushrooms because they have similar battle properties. (I assume they're flammable, weak to cold, etc.) Besides Grass doesn't literally mean "grass", the only pokémon that is literally grass is Oddish. It's the "Nature" type.
>>32353701Spiders aren't insects, but they ARE bugs, as are scorpions. Bug is just a common non-scientific word for creepy-crawlies. Like how 'bunny' is just a cutesy name for a rabbit, rather than an actual scientific name for a baby rabbit.
>>32353718>serpentineSerpents were often associated with dragons in western European mythologies, in part due to all the sea serpent myths. This is why Draco Malfoy in Harry Potter is named 'Draco', meaning dragon: because he's a Slytherin, and dragons and snakes are connected somewhat in general folklore. Oriental dragons are also notably serpentine.
>reptilian or avian PokemonIf it's a reptile as well as a Dragon type, I think we can give the benefit of the doubt that it IS a dragon, however it may look.
I don't know what you're smoking that you think any bird pokémon besides Altaria is a Dragon type, but Altaria is based on a Peng which is a mythical dragonish bird.
Most other Dragon types have that type because of a pun, or the animal/plant they're based on has "dragon" in the name. Kingdra and Dragalge are Dragon types because seahorses are called water dragons in Asia, Flygon is one because antlion adults are nicknamed "sand dragons", and Yanmega isn't one because they aren't called "dragonflies" in Japanese.