I made a platform, gml-raptor, on top of gamemaker studio which helps greatly, not only for jams. Art and sound are taken from asset bundles I own and this game has less than 300 lines of code written exclusively for this game. I made a good plan and design on paper (planning does not count towards the 3 hours) and when I bootet up the in PC it was done quite fast.
Raptor is available here at itch through my profile. I invite you to take a look at its wiki so you get an idea how powerful it is