Overall a really fun solid game. The sprites were cute and easy to read, the use of black and white was well used to differentiate foreground, background, and characters (not an easy task), and the physics were a natural experience. Here are some things I think should be reviewed:
1.) Personally, when spacebar is used to jump, I prefer to use the arrow keys over WASD for movement, that way I can use both hands. That may just be a personal preference, but most games I've played allow for both.
2.) Implement some sort of flashing or fade out when the player is damaged, returning to normal when the invincibility is gone; It was hard to time when my invincibility is over, and this will also help differentiate between enemy and player damage since these two make the same noise.
3.) There was a strange bug where when I hit ESC and selected to exit, the game just continued, the character froze in place (not interacting with anything) and key presses did not read.
4. ) I enjoyed how respawns worked. That being said, I couldn't tell if I was supposed to avoid the enemies or clear the enemies before proceeding. Because ghosts wouldn't go back to their original position, they would block paths and then I'd have no choice but to take damage.