-When facing the first Allosaurus on your way to the facility when you are first using Regina, buy the Flamethrower and go to the ledge that leads nowhere towards the west. Every time it approaches you, burn it. This way, it can be killed easily and you will get a large No Damage bonus.
-To kill a Allosaurus easily, purchase the flamethrower and keep aiming at its head. It will eventually die and give a huge no damage bonus if you did not get hit.