And here's the antagonist. If you have HC ideas, tell me!

Strike (nickname, his real name is Vlad) is a multiturfling, taking parts from Inklings, Octolings and even Jellyfishes due to some of their tentacles being on it's back.
It is the creator of the FlowCharge, a special type of ink that mind-controls people, cannot be wiped out if the turfling is splatted, and allows the person to use every Ink Flow that exists, but with a much weaker effect.
The only way to get rid of FlowCharge is water, as it'll act like a second skin that protects turflings temporarily from water.
He kidnapped Abigail to charge her (infuse her with FlowCharge), who let Mike with a rage against him.
During the assault, it tried to blast a FlowCharge ray at the group, but Yukiko stepped in front of the team and took a huge part of the hit. This made the tips of her tentacle hair red.
She got charged, too, but the team was fast enough to throw her into the water.
During that time, Strike escaped. His location is currently unknown, and Hinata is on the hunt for any hints pointing ou where he is.
Switches between that gas mask and the Parallel Cannon mask to hide it's face.

if you want to know who Abigail is, she's Mike mother.

This is nice! Unfortunately I don't have any headcanons :<

No prblem! That was only if you had some ideas!