If you're struggling to defeat the first boss, I think i figured out the character you need to use: Lance.
what you should do is just buy him, then play the boss. always go in as close as you can to the boss before using his sub-weapon. if you use it four times, it knocks the bush down to AT LEAST 50% health. then just use the normal shot till you can use the sub-weapon again. (at least 25% charge) eventually, you'll kill the boss. That's only if you want to use my strategy, but do whatever works best for you. (not tested with Handicaps or Cheats)
I first found the "throw backwards" glitch a year ago. my friend told me to do something (of which a i forgot) to get out of this. wasted the next five minutes of class racking up my score for no reason at all. :P