I really like your two world mechanic. Looks like it was way simpler to create than the mirror world I (kinda) did in my game. Visuals are simple, but work without real need of being more complex and the music and sound effects are good. I just had some trouble with the controls partly because there were no right hand/arrow keys implemented, but mainly because I kept hitting Space to jump by mistake, especially when in hurry to jump before the platform disappeared (from hitting Space). I think a different key would have worked better to switch worlds. My suggestion would be Shift (both Right and Left if possible) because not only is it a common control key, it also fits what being done (shifting reality).