I have to say the random levels difficulty is VERY inaccurate. I get a hard level I only solve after 3 hints and I press "harder", guess what, I get a level with 3 black stars lined up so you could shoot all of them with the main star, I press "harder", I get a level that is spammed with green stars... and then I press "easier", I get a hard level that I solved only after 3 hints...
Secret Levels 1, 7, and 8 walkthrough:
Secret Level 1- Level 1, Go to the top right section (The one with a very tall wall) and fall off to the ground.
Secret Level 7- Secret Level 1, go down (all the way through the blades), hold left then jump and you will see a door (on an invisible platform)
Secret Level 8- Secret Level 7, just below your starting brick.