Honestly, fire mons must be the hardest to design. For a water type, just go fishing to find some inspiration. For a grass type, either you:
-Take an animal and shape it like a plant
-Straight up make a plant
But for fire types, there isn't any kind of animal producing fire, and rare are the objects that can use/create fire. so GF can only make:
-Any animal with some fire slapped on ( Chimchar, Charmander, Cyndaquil, the list goes on )
-Lava ( Magcargo )
- Dragons
I think that's why so many fire types look uninspired. Ninetales, Charizard, Arcanine, the list goes on. They are just basic animals that were given a fire typing ( no, dragons aren't real but come on ). Nothing else really makes them interesting ( beauty doesn't count, these are supposed to be pocket monsters ). Yeah, Ninetales is based on folklore, but that doesn't sell it to me.
Of course there are exceptions, Magcargo, Darmanitan and Magmar all share interesting, creative and original aspects.
The fire type is weird for me. On one hand, I feel like it absolutely needs to exist because of how elemental and symbolic fire is, but on the other hand, there isn't a lot that you can do with it