Love the atmosphere in the game , both idea, music and graphics are great!
If i should comment on anything, it would be to work on the character controls.
There are a lot of good tutorials on improving 2d platfomer controls out there.
For example being able to control the height of a jump by letting go of the jump button is a great start.
Also i would like to get a hint on when to press jump on the mushroom. A sound or graphics countdown or something.