Basically I want my sprite to have a temporary speed boost by holding down the shift key + movement key(s). I want the speed boost energy to naturally recharge slowly over time when not in use, and to deplete quickly when used.
I don’t necessarily need a step by step tutorial, I’ve figured out how to make parts of it work… mostly I’m just looking for a link to a game that already incorporates this kind of mechanic, then I can (probably) figure out the rest on my own by viewing their edit screen. 
EDIT: and yes, I have already searched the forums and Google, still haven’t found exactly what I’m looking for.
