MRWalker,
Thanks! I have uploaded a new version with a bunch of improvements. Let me know what you think.
Improvements:
1. I tried to fix the collision detection as good as I could for now. Fixed for the character and bullets.
2. I made the easy difficulty have the falling jump with the medium and hard difficulty omitting it. The standard difficulty is now medium instead of easy in order to take the falling jump away from the start of the game. An easier difficulty can be selected upon resetting or a page reload.
3. Added path to third level on the second level. This means that you can make it to the third level in the game without ever defeating an enemy or boss.
4. Enter or space can now be used to start the game and retry. No use of the mouse is required once the flash been clicked on.
5. Removed information about falling jump in the instructions.
6. I fixed the pipe glitch in the third level and added the ability to buy super mushrooms in the third and fourth level. Walking to the left through pipes had to be kept in case an enemies coins lands in front of the pipe (meaning no way to get to it).
7. Populated third level with more enemies and items, still haven't created the bosses for this level yet.
8. Added a path to the fourth level at the end of the third level.
P.S. Fourth level has not been constructed, once I finish the bosses for the third level and work out all the fine details then the fourth level will be created.