I believe the game is playable to completion, barring any strange bugs that I haven't found in playtesting. If you're stuck and can't figure out where to go, here are some hints:

I HAVE THE MAIN CHARACTER COSTUME:

- Try collecting coins and the rainbow substance to purchase a costume

- You can change costumes using the control, shift, Z or C keys. (B on a gamepad)

- You speed, jump height and gravity are changed with you costumes

I HAVE THE PLUMBER COSTUME

- Your jump height is increased

- The plumber can take out enemies by jumping on their heads just like a certain other unnamed hero

I HAVE THE NINJA COSTUME

- You can use the special with the down key

- You cannot kill the boss at this point of the game, better to run away.

- You can teleport THROUGH certain thinner objects that might otherwise hurt you.

I HAVE THE ROBOT COSTUME

- His special is a multiple jump in the air (using the special key, not the jump key)

- You need 2 rainbow objects to buy the next costume. They are all located in the upper left quadrant of the map.

- Try going left from the starting area

I HAVE THE KNIGHT COSTUME

- You will need to use the ROBOT to get back to the area in order to progress

- This area more than most will require you to switch back and forth between different costumes

- Shovels are great tools for breaking blocks

- You need 2 rainbow objects to buy the next costume. They are all located in the upper right quadrant of the map.

HOW DO I FIGHT THE BOSS?

- Just wail on the guy. Mash that special button and you'll get him good :)

I WANT TO FIND THE SUPER SECRET HIDDEN ROOM WITH THE MYSTERIOUS SOUND FILE EASTER EGG!

- Examine the main bad guy from the menu screen. You'll get there.