>>51523349Kartana, because Saturn is the god of agriculture and his symbol is the scythe. Celesteela is based on a Japanese tale about the moon, but it is also Uranus, who is the god of the sky. Hence Flying Type and being a rocket.
Also, the Pokedex numbers of the UBs are LITERALLY all in the exact same order as the planets starting from the sun and going out. The only difference is Buzzwole and Pheramosa being swopped. Idk why that is but it seems like a yin yang kinda thing.
The planets also have symbols the UBs may or may not incorporate; I haven't researched that part enough. Mars's symbol is the spear for example, which seems to be referenced by the mosquito nose.
Lastly real quick before my phone battery dies—Nihilego is mercury the god because he is the messenger of the gods to mortals, and is "the god of boundaries", hence it being the first UB to start invading in the story. Niheligo looks like a little girl because the element mercury in alchemy is considered feminine (and its symbol is just the "female" symbol with a little hat on it). Speaking of hats, aside from the god mercury's iconic winged sandals, he had a winged, brimmed hat, like how Nihilego is literally a flying hat. And finally Nihilego is based on the phrase "mad as a hatter". 'Mad hatter' became a phrase after an incident where hat manufacturers put mercury in their headwear and as a result a shitton of people got mercury poisoning and went insane. That whole part of the story where Lusamine goes batshit crazy is one big fantasy version of mercury poisoning. Mercury is especially harmful to the brain and nervous system hence the jellyfish-ness.
You won't find THAT on Bulbapedia, no sir....