Really interesting concept!
I really liked the mechanic that was introduced here, also the movement felt really responsive and interesting to play with. The game was quite hard at some point, since it was quite hard to move or jump while pressing Shift. Perhaps a toggle or allowing players to rebind the controls could be a solution for that.
I also would've liked to see some sound design. Maybe a cool track or some sound effects.
Nevertheless, great game. Would def like to play a more polished version in the future!