Multiple monsters can never be driven to extinction. Therefore, try to get one kind to go after the other. When you fight a monster use fire, electricity or acid whenever possible. Prefferably use all of the above. And an atom bomb.
ALL atomic weapons cause normal creatures to grow huge and carnivorous.
As do all chemical and germ weapons. When you say it looks like you made it, be prepaired to die. This always happens and should be expected. Stay Asexual during the course of the movie, you'll be safer. If your friend who is being turned into a creature of the night, tells you to run, do so, he or she is fucked and there is nothing you can do about it.