To reiterate a quote that Sparen took from me on Skype, my advice to all participants is to
MAKE YOUR BOSS FIRST!!Pretty visual effects, including 3D backgrounds, custom charge effects, explosions, boss auras, and lifebars are by no means essential or even necessary. All of these effects will mean nothing if your boss's attacks are hastily made and/or boring. The only visual effect that I would consider absolutely necessary is an image to represent the boss, just so it can be seen and aimed at. It doesn't even have to be animated.
My recommendation is to finish your boss battle completely before you begin to invest any time into special effects, like a background. Remember, Danmakufu DOES have some default effects available to you, especially v0.12m. Both versions have default systems and backgrounds that you can use if you run out of time to make your own. If, however, you spend lots of time on cool effects and run out of time when making the actual boss, then you're unfortunately out of luck. It doesn't matter how pretty your boss looks if it's incomplete.
Finally, remember what Drake said in the opening post:
gameplay, i.e. good pattern design and being fun to play, is more important than presentation and aesthetics. As usual.
Do not get discouraged if your script doesn't LOOK as nice as someone else's. While everyone may not be capable of making pretty effects, EVERYONE should capable of making fun and creative patterns, which is the true goal of this contest.
P.S. I by no means mean to say that shiny effects mean absolutely nothing. They help make a script more fun, to be sure. However, they are more comparable to icing on a cake.
Edit: Someone asked me to also touch on the use of ADD rendering on special effects and bullets alike. A common mistake that I've seen scripters make is making their patterns and effects TOO shiny. Overuse of ADD rendering can make it difficult to see important parts of the screen and are often just hard on the eyes in general. It's fine to use ADD rendering, but try not to use it TOO much. This is something else that can possibly be avoided by saving special effects for last.