Firstly, since it is possible people will only look at the first line, there is no preloader. I didn't exactly plan to have one in the first place because I was using Kongregate's Shootorials and they didn't really mention anything about a preloader . . .
I didn't really think it needed one though, it is only like 450 KB.
This was pretty much my first real project into ActionScript 3 and it taught me quite a bit so I hope you like it.
The sound effects are from freesound.org
EDIT: There was a little error that I fixed, I just had to change the value of one variable. It made the final boss appear before anything else.
I fixed it so you can't go off the screen, but it might take a while for the file to update.