Good use of theme gravity + control. This kind of game need very precise jumping, and sometimes, it's not enough permissive (need coyote jump). It could be interesting that the background use a logic to identify immediatly caracteristics (use arrow bacground to say gravity up/down, and 2 background colors to say regular/inverted jump, for instance). Though, I like the idea of infinite runner, procedural generation of level. Well done.