There are two things I think need to be changed. 1. The droids should be affected by the coin magnet. They fight for you, the coin magnet should work for them as well. 2. After you beat a boss, the rockets it fires should go away as well. I was fighting the 5th boss, beat it but died because I got hit by rocket it had fired before I killed it.
For those who didn't know. This game copies a game called Battle City, a Famicom Game only released in Japan. Putting in Mario characters and making it a flash game probably wasn't the best idea to introduce it to the rest of the world.