One side, one jump
A game in which you play as a one-sided shape who can only jump once per level, which takes place on a one-sided surface (a Möbius strip). (There's also only one color and one note per screen, and the levels are numbered in unary.)
I made it for the 2019 Game Maker's Toolkit game jam, with the theme "only one". Once the jam is over and judging is done, I might add more levels.
Controls: arrows to move, Z to jump; or WASD to move, J to jump. P to pause.
Also playable on my website.