So @raspberrydaisieschlb setted the 28th of May to be an Allan appreciation day and I wanted to post a drawing but It came out shitty... So I'm gonna post my headcanons instead!
Allan ended up being Mercury, not Gavroche .
He was about to name his Superhero persona Gavroche tho. So the rest of Quantic Kids (mostly Melodie) usually calls him "Gav" instead of Mercury.
He and Allegra were the first Parisian superheroes of their generation
He has his superpowers since birth. When he first discovered them, he caused a Minor Car crash
Having super speed infulences his health in a bad way - he burns calories real fast, (fun fact: I was trying to draw him looking at the mirror with his shirt up, freaking out how much of a skeleton he is) and although he has some nice leg muscles, they're very weak and he can't walk/stand for too long when he's outside of the suit.
Has a family in Rome (cuz Mercury is a Roman equivalent for a Greek god Hermes)
Would totally dance if his legs allowed him to do so.
Occasionally medites and he tought Allegra how to do that too.