I actually had a few thoughts on Dragons. Being reptiles, most of the type chart makes sense already. Reptiles are found in every biome and climate, from the hottest desert to the rainforest to the ocean. The only places you don't really run into them are areas where it is inhospitably cold. As for why Electric types don't hit them effectively, I don't know. Perhaps their natural ability to absorb energy extends to electricity? Fairy being immune is just nonsensical, but I could see a resistance being justified somehow. On the offensive side, the energy a Fairy-type emits could just be incompatible with their biological systems, causing a sort of "energy poisoning."