So, although a thread like this appeared a bit ago, currently one of the things I am totally obsessing over is Geometry Dash. It's a pretty hard game inspired by The Impossible Game, but with more difficulty, different modes, and customizable cubes, amongst other things. Really it's just a better version. I've completed all but 3 of the main levels (being Clutterfunk, Clubstep, and Electrodynamix), and I just completed my first demon level!
Nice, all the demon levels I have done. Demon mixed. Y-step. Club step. Cyber paradise. And some others I cannot remember at the moment. I completed all the main levels. However I did not get all secret coins for some.
You should probably do The Nightmare and The Lightning Road, those along with Demon Mixed are considered the easiest demon levels as far as I know.
I tried to get my older sister to buy this game for me, but she said it was a waste of money. She bought me Frozen Free Fall instead. And may I say, this Frozen game is a TOTALLY WASTED AMOUNT OF MONEY