What MLP character do you think would be what TF2 character? I think (and I'm taking idea's from a comic-artist):

Rainbow Dash - Scout

Derpy Hooves - Soldier

Spike - Pyro

Pinkie Pie - Engineer / To all who think it should be Pyro, the original set-up was from way back when Pinkamena was more relevant. Pinkie has proven herself to be one heck of an engineer. Party Cannon any one? Or what about that helicopter she made in Gilda's first episode?

Big Mac - Heavy

Applejack - Demoman / An American accent does not make her and Engineer the same character. Seeing how robust Applejack is, I think Demoman suits her more.

Twilight - Medic / Fluttershy wouldn't be a good Medic, because she would be too scared to actually be in the heat of battle. Something a good Medic has to do. Experimenting on his teammates? That sounds a bit more like Twilight.

Fluttershy - Sniper / Fluttershy would be away from the battle.

Rarity - Spy

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Rainbow Dash- Scout
AppleJack- Engineer
Derpy- Soldier
Bulk Biceps- Heavy
Fluttershy- Medic
Twilight- Sniper
Rarity- Spy
Pinkie- Pyro
Spike- Demoman

That's how I always see it.

5484413 Its formation and without nexus. MLP has proven that applejack can be engineer, fluttershy is better to heal.

5484504 this training makes more sense.

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One upon a time, a few years ago, I thought for a bit and came to the conclusion that if you wanted a team of badasses, you recruit from the best and mind-control the ones who resist.
This was the result

Scout: Firefly is still fast.
Soldier: NMM is crazy, and quite likely to use high explosives at close range
Soldier: Celestia. Sun. Fire. 'Nuff said.
Demoman: Discord and his explosive chocolate milk. Big booms for all.
Heavy: Sombra...he's weird, doesn't talk much, and missing a few marbles.
Engineer: Twi is smart, so she can probably create much of the stuff, and more. Plus, that pendant has a dark secret...(Glows Loyalty Red)
Medic: I've read a story about Nurse Luna. Really, the only reason. Plus, I'm kinda using a lot of Alicorns or just powerful beings.
Sniper: Cadence....I ran out of alicorns for the pic. Plus, she looks pretty badass with the hat and rifle.
Spy: Chrysalis. Disguises. General ass hat. A no-brainer.