For those who watch "TF2 Analysis", I have a theory.

Fire Brand, who plays as the RED Medic, is actually the RED Spy.

Reasons: He never heals anyone.
Is easily beaten (Low HP)
Pops up out of nowhere.
Barely puts up with others on or against his team.
Doesn't even fight most of the time.
Antagonizes everyone he meets on a minutely basis.
Is pretty useless in MVM (Why can't you sap a bleedin' TANK?!)
And lords his position over A&Y (And by extension, Mad Munchkin.)

Or maybe he's just a lazy Medic who does nothing but piss everyone off.

I dunno, what do you think

5666984 You have to send him this theory!

5666984 If he's actually the red spy, why hasn't he impersonated an enemy or stolen any plans?

5666997 I would I fi knew how
5667465 Well, he could've been the original BLU Spy, disguised as the RED Medic, and just forgot. That raises the problem of Thespio, the BLU spy. The reason why he hasn't stolen any plans is because the game is set in MVM, which doesn't have any CTF rules or objectives.

So, as some players may or may not know, Spies can disguise as members of their own teams, so maybe, having gotten used to acting as the RED Medic, chose to be the RED Spy after Gibbons left to become a Pirate. So that there wouldn't be a problem (As the rules of the game, apparently, is that there can only be one pony (Or Hippogryff in Silver Quill's case) per position (18 maximum, one person to fill the nine mercs on two teams.)
So, having taken the position of RED Spy, he threw on the disguise of RED Medic, so that no one would suspect that he'd been lying.

If that came to light, A&Y, the RED Demoman, could assert his "Genuine German-ness" and play Medic. Then, Mad Munchkin could be the RED Demomare, as she is Scottish.
A&Y complains at least once per episode about how Fire Brand isn't right for playing a German Character. And in the beginning of "Seven Nation Army: the movie", she complains about how she would be a better demoman.

In "To be or not to be..." Fire Brand says to Thespio "Oh. Ugh, really? Tie me up and dangle me over a pit of Lava sharks? Okay, you know, that'd be slightly threatening if you weren't cutting the rope with the Freaking Conniver's Kunai. You do know that is the worst Spy knife, right? And since you lack the finesse to face that fact, you are completely use-"

In "Seven Nation Army" Fire Brand says to A&Y "Ugh, we've been over this. I'm the Medic, so I get first pick because I made this team! Why is that so hard to understand?!"
From this we can infer that Fire Brand has ample time to choose his class, the Spy, and then disguise as the Medic.

A&Y replies "Look, my German-ness is the one thing I've got that no one else has. And the way you play the Medic is a disgrace. I haven't seen you heal one pony since we started this team."
Emphasis is obvious, as A&Y would have an eye (Or, at least the one not covered by an eyepatch) on Fire Brand at all times.

Mad Munchkin says to them "Oh really A&Y? You want to talk about an absolute disgrace? Every time I hear you using a Scottish accent, is like listening to Horseshoes scrapping across a chalkboard. I'm the one who should be the Demopony on this team."

So, in effect, by lying to his own team, he can lord it over two other players.

Now, if it did come to light that he was, in fact, the RED Spy, A&Y could be the Medic, Maddy could be the Demopony, and... well, that'd open up the position for RED Soldier.

5669001 I don't know. Josh Scorcher is from the Marines. You'd think Firebrand would be a sniper, heavy or demo.

5669175 I wouldn't know, I mean, I work in a library and I'm a Heavy Main.

5670956 Well there's no librarians, accountants or desk clerks in this game. You have to play someone else.

Of course, accountants can be pretty dangerous.

5671685 Well, if Civilian had made it through beta, there could've been.

And Librarians are dangerous. Intelligence and heavy books of bashing.