Regarding the Mascot Characters...

[Agent Z]

It seems like in every form of promotional media, such as the newest screenshots for the Splatfest-only map, the same eight squids show up, and it's always green against pink. The most recognizable of these squids is actually on the right side of Squidboards page wallpaper; a pink, short-tentacled Inkling girl with a king tank top, blue shoes, a king flip mesh, and using the Dualies. Although I have noticed that she never seems to be wearing her hat in any of the screenshots. I get the impression that these are supposed to be the playtesters personal loadouts, or the developers maybe. Either that, or this is just me overanalyzing things against because I ran out of coffee and am slowly getting more restless as the hours drag by like an Inkbrush through Toxic Mist.

But uh... Really, who are they supposed to be?

Also, the "canonical" Agents 3 and 4 are a green Inkling girl and an orange short-tentacled Inkling girl respectively. Yet in Agent 4's case, that only seems to be true for promotional art, because the trailer showed about 10 different Agent 4s (probably because multiple people were involved in the trailers). Not sure why I brought that up, my mind just wandered out of the place it was supposed to be and right into the gaping jaws of procrastination disguised as a tasty meal from Crusty Sean's, and silly me I decided to eat the thing without knowing that somebody shoved an Ink Mine into it.

 

[TheScout]

Maybe these squids were concepts for the Amiibo? The girl with short, pink hair doesn't have her hat on the amiibo either. This makes me think these are probably hand-picked "best-ofs" that the dev team put together for use in the promotional art, so that they wouldn't have to decide what to put in each individual piece of artwork.

I don't think it's anything of note as far as the lore is concerned.

 

[Lyn]

It's likely just a generic, recognizable Inkling character for the promotional material, same as the first game.