In almost all levels you can get thousands upon thousands of extra points easily. First what you need to do is have a buch of extra credits. Then when you encounter one of those things that let you come back there when you die, and make sure you have killed everything behind it and near it. Then hit the thing and die purposely. You will go back to the thing and all the enemies will be back. Then run back as far as you can go and kill everything. Please note that this doesnt work on all continue points but it does on most of them. If you die this can be quite time consuming so try not to die.