Hint: If you're stuck on any one particular 'monster' on this game, it's worth remembering that as long as you killed the monster before you died yourself, it will not return to get you again when you restart the level. Because of this, really difficult monsters can be irradicated by running into them on your first life. When you return to the level, one life down, the monster won't be there and you'll be free to continue the level.
