I'm gonna be a bit wishy washy with some of them, likely only taking a trait or two from each. I'll probably throw some mythological influence in there too, like hydras, minotaurs, unicorns, etc.
But for Marchosias I'm looking at animals like boars, canids, and various reptiles.
For Vepar I'm considering sharks, anglerfish, sea jellies, crabs, and eels. Also cephalopods in general.
Gremory's got spiders, a few birds, maybe a specific kind of bat or two.
I was thinking that a wasp motif cold really fit Gremory if it’s used right. If mammals are a consideration for vepar, narwhals might be an interesting counterpart to the unicorn. Sticking with the aquatic theme, it for a poison heavy vepar route, have you considered her sitting on a large anemone for when movement becomes… challenging. With a few prominent tendrils in the design making her method of attack visually clear?
I'm actually holding off on insect themes just in case I get around to uhhh something else.
But Vepar's poison-heavy route (Creeping Death) will give her a blue-ringed octopus aesthetic with barbed tendrils, so she'll maintain a clear method of attack. I like the anemone idea, though, I may use that for her base buildings or something!