You're playing as Low, a small character working through 32 pixel-art levels, and the goal in each one is the same: grab five coins scattered around the stage before the golden trophy at the end even shows itself. Miss a coin tucked behind a spike wall and you're backtracking through a section you'd already cleared.
Springs, moving platforms, wings, and a floating umbrella show up as you go, each one solving a different kind of gap that regular jumping can't clear. Later levels start layering these together, so a single stretch might need a spring-jump into a moving platform, then an umbrella glide to stick the landing. Boss fights cap off certain worlds, and they hit noticeably harder than anything leading up to them.
Controls: Arrow keys to move and jump.
Anyone who grew up on old-school browser platformers will recognize this one's DNA fast. Play Low's Adventure 3 unblocked at classroom6x and see how many of the 32 levels you clear without losing a coin.