Humanoid! Xolotoro (King Salmonid)
For very yaoi reasons this form exists HHHHHHH
I did type out some backstory about him in a post's comments and I'm just going to copy paste it here... hehe
: His 'boss name' is Xolotoro, and like how you guys call Horrorboros 'Boris', he is called Xolotl!
The idea is basically that he was a Geiji (like smallfry)(fyi geiji is a irl sort of 'bycatch salmon' which haven't put their body reserves into reproduction yet, thus is very fatty and tastey. In Splatoon salmonid logic, that means they are very powerful/have incredible potential) who climbed to the peak of where the waterfall (where they train Horrorboros(plural)) came from, and he basically 'ascends' into an actual dragon, the potential in him transforming him into something that's 'beyond' a salmonid, yet still a salmon.
After he ascended, xolotl basically just flew off on his own and does whatever he liked. He is still influenced by Salmonid Culture and believes in similar things about being tasty, he just dosent see Salmonids as 'equals'/'his people' anymore. Xolotoro is one of a kind.
Sometimes he fly over/pass by Salmonid villages, and the salmonids gathers the golden oil he drips and uses it for cooking
So by definition he's probably a Mythic, but he shows up in the context of big run, so I call him a king salmonid anyway
: The way he have a humanoid form involves another oc of mine called Corvus (Octarian) who's a shady underground info broker sort of guy and 'makes himself too useful to get rid of', and with this he have a pretty large degree of freedom even when he's underground (literally) and his share of connections and wealth. Since octarians have trade deals with salmonids for power eggs, Corvus is in on the business too (he actually learnt how to speak salmonid) and he heard from the salmonids about this Dragon Salmonid that rains Golden Oil that's really tasty.
And Corvus was immediately (golden power eggs that they won't trade->golden oil described as really tasty=really powerful substance in Salmonid logic?) and invested fully in tracking down Xolotoro, and trying to trap it to harvest its oil. Because he can employ a bunch of people to do work for him and have access to octarian tech, the traps *does* end up working for a little bit, and that's more than can be said about anything Xolotl have ever killed (nothing really puts up a meaningful fight for him anymore) and Xolotl is really fascinated by this, especially since Corvus just turns out to be a scrawny ass octoling. Corvus managed to strike a deal with Xolotl from these grounds, and because salmonids have incredible adaptability, Xolotl is able to 'adapt' his body into a very octoling-like shape to stay closely beside Corvus!