Beat The Slime Boss
On the Slime boss level, everytime you shoot the slime monster it shrinks down into his trash can. Shoot the slime monster untill it's whole body is in the trash can, it will loose energy by doing this but each time it goes down into the trash can, the slime monster gets bigger so it takes more time to shrink it down. Just get it down in the trash can about four times, then it will die.