"I assure you that the extra with the hat in the last panel is certainly not intended to resemble anyone in particular whatsoever, though it is apparent that he is a man."
Shive admits that Susan's line here reminds him of the speech patterns of River Tam. Not to mention it's caused by a "serenity spell".
And in the strip before that, Susan's Awakening looks a little like she's turning into a reverse Super Saiyan, at least if you ask me.
So Immortals effectively die and are reborn in different bodies with different personalities? Sounds like a certain immortal doctor.
Speaking of which... Panel 3 of this comic. Take the glasses off that man, what do you get? That is the Eleventh Doctor, bowtie and all. According to Dan Shive, the resemblance was "amusing, but it wasn't something I planned". However, there's a good reason why that's probably not THE Doctor:
Dan Shive: If defying the laws of physics made Doctor Who cry, he'd never get anything done.
The title (not shown in the new website layout) of this comic is an obvious shout out to the main character of fellow gender-bending webcomic The Wotch.
It has been mentioned in-universe that the most obvious superhero name for Grace, Squirrel Girl, has already been taken by Marvel Comics.
Agents Wolf and Cranium are a subtle reference to Mulder and Scully from The X-Files. Aside from their job, and their appearance, the names "Wolf" and "Cranium" are possibly stealth puns on "Fox" and "Scully".
At an interview at Susan's video store, Elliot meets Mister Tensaided, who makes a blatantMatrix reference...which goes over Elliot's head completely.
Tensaided: I think he should be condemned. He has serious metal fatigue, his wiring is substandard, he's completely inadequate for our sales needs, and his brain is like a demilitarized zone.
Susan: Are...are you paraphrasing a Ghostbusters quote about a building to describe a person? How does that even—