Most Aliens can be killed, with only one weapon. Some aliens thou take alot of weapons to kill them.Fir- st theres the basic alien.The basic alien of course are the hive catchers.These aliens are the ones who go and get the hosts.These aliens can usally be killed with a basic short controlled pusle fire rifle blast.The seco- nd kind of alien is the cacooners.The cacooners cacoon the host.Thes aliens are very weak these aliens can be killed with a pistol.Next is the face hugger.They are the weakest but there very sneaky.A simple pistol or a little bit of fire, can kill them easy.The next alien is the guard alien the guard aliens are a little strong er.About 50 or so pulse fire shots will kill them or m ost of the time get close to killing them.Shoot them with two grenades.Or about 5 oz of fuel and there dead. The next alien (i dont know there name) is the aliens that can crawl on the roofs.I call them crawly aliens. These aliens can be killed with about 150 pulse fire sh ots.Pulse fire shots arent very effective.1 grenade sh ould kill them matter of fact its a little much.Some fl ame about 3 1/2 oz can fry em to a crisp.The next alien is the dog alien.These aliens are very ahrd to kill these aliens are extremly fast.Faster than any known aliens.Even faster than the face huggers.These aliens are hard to hit with any weapon.Thats why you have to get lucky.With a pulse fire rifle you can try to hit th em but its likly youll miss them.A gerande would kill them but youd surely miss.Grenades dont go fast enough. The best way to kill them is to trap them in a corner and flame em.This is very effective if done right.The next alien is the queen.The queen is extremly hard to kill.It takes along time.First burn her eggs,so she wil l get off her pipey thing.Then use a pulse fire rifle. Unload about 5 to 8 clips.(there are 150 shots in a clip).Then unload a crapload of gernades in her and run the whole time.Also if you have one use a smartgun.The smart gun is also good for the dog alien.Because it sp reads so well.While killing the queen dont forget to reload.In alien 2 or aliens.Ripley blasted the alien out of the ship and into space.This works but its har der than it looks .So thats the best way to kill an alien.