According to Shigeru Ohmori UB are based on the idea of invasive species.
We actually know the references for some of them but we're still missing some.
So if you have any idea feel free to comment ^^
What we know:
-Nihilego is based on Phyllorhiza punctata an invasive species of Hawai (jellyfish)
-Buzzwole is based on Aedes albopictus an invasive mosquito
-Pheromosa is based on Periplaneta americana an invasive cockroach
-Celesteela is based on Princess Kaguya from the Japanese legend The Tale of the Bamboo Culture (it is known as the first historical mention of an alien)
-Guzzlord is clearly based on black holes
-Poipole is nearly an occidental representation of an alien mixed with a larva of wasp
-Naganadel (especially clear when shiny) is based on Vespa velutina an invasive hornet
The ones unclear:
-Kartana (known as a deity in the game, based on origami/katana ???) Can be a criticism of humanity destroying nature and deiting himself?
-Blacephalon (???)
-Xurkitree (live in jungles, electric tree)
-Stakataka (I know everyone thinks about Trump wall but it reminds me Block Bots from the seventh movie (based on Rayquaza vs Deoxys)) Can be a criticism of nanobots
Any idea?