A red hot chili pokémon with fangs that would be the first official grass/fire type with an ability that acts like Destiny Bond on any opponent using a biting based move. Or a Wicker Man with the same typing. I've had this idea since 5th Generation so don't go taking my idea without telling me since I have some design ideas.
Not to mention a Leprechaun that should rightfully be dark/fairy obviously.
Although not the first time, the Tapus imo have played an important staple in showing Game Freak's design tapping taken into account outside of Japanese mythology and I would love to see them take it further into realms of Germanic, American, Greek, Egyptian/Bablyonian/Assyrian/Mesopotamian (Pazuzu) and Celtic characters (Wicker Man).
As most of you are aware there are encyclopedias full of natural history - zoology, paleontology, botany and even microbiology that they haven't even touched for influence despite their already impressive run so far combining these two areas of design (natural history and world mythology). Shame on them is deserved that they couldn't be arsed to expand the fossils this generation despite the fossil site appearing incredibly early, its such a deliquent, backward decision by them. We could have had a badass dromaeosaur by now from them...
Last and as opposite the least as you can get, theres always the Cthulhu mythos, but then talk about tempering with power creeping because they would be easily the most powerful pokémon in both in and outside of existence despite having one Outer God already in this universe by the name of Smeargle... and they should all be ??? type.