At the very last planet, you will face amutated proto-pet. This may sound crazy,but let it get a ammo box. For example: If boucers or any other kind of weapon comes flying out of its mouth, you must get under the mouth of the proto-pet. The weapon won't be able to hit you there. While the proto-pet is still firing the weapon, it will leave you a clear shot so use the time wisely. On the other hand if you get the ammo before the proto-pet, it will fire more proto-pets leting you be a locked on target.