- Headcrab -
Small, harmless creature. When it comes within 10-15 feet of you, it will jump and try to latch onto your head. To easily defeat this, just hit it with a crowbar like you would a baseball using a bat. Watch for these in darker areas, and they usually are found in packs.

- Zombie -
Slow moving and lifeless creatures, the zombies are what happens when scientists get "headcrabbed". They can only swing thier sharp claws at you, but they casue a lot of damage. Three headshots with a pistol will kill one.

-Bullsquid-
A small creature with tentacles over its mouth. Besides a melee attack, the only thing it does is spit acid at you. A few pistol shots or one accurate shotgun blast will kill it. They are usually found alone, feasting on human remains.

-Houndeye-
This is another small creature. It is almost as harmless as the headcrab becasue it only has one attack that is weak and takes a long time to power up. It makes a high-pitched noise and shakes in one place right before releasing a shockwave that can minorly hurt you. One shot from the magnum, two or three from the pistol, no problem. They travel in packs.

-Slave-
This three armed, green, one eyed creature can release a very harmful lightning bolt. Yuo can tell when it is charging it's attack, so either move behind a barrier or kill it. These are most infameous for randomly teleporting into battle and traveling in packs. Usually two shotgun blasts will kill it.

-Barnicle-
An easy to aviod threat, all it does is attatch itself to the cieling and let a tentacle down to strangle unsuspecting (and dumb) victims. No, it's not a rope, Half-Life doesnt have ropes, so look up and place a few pistol shots into it.

-Grunt-
The military is sent in to Black Mesa to control the events going on. They are extremely smart and quick, so moving around while crouching so they can't hear you is a good idea. Quite a few 9mm AR shots will take one down, even more pistol shots, a double blast from a shotgun is the best until you get the energy weapons. They have melee attacks and either shotgund or automatic rifles. If you're camping, listen for the sound of a grenade hitting the floor, because they are not only accurate with them, but know when to use them.

-Turrets-
This is basicly a grunt with increased firepower. It is not mobile, just a guy standing behing a big gun. Once you kill the man controling a turret, the turret wont shoot anymore. To avoid the rocket launching turrets, all you need to do is strafe left and right.

-Alien Grunt-
This is the backbone of the Xeno army. They have special hornet guns, which can seek to an extent. They aren't nearly as smart or fast as human grunts, but they don't go down easy. Three shots from a gluon gun or about a second with the egon gun will take one down.

-Assassain-
These chicks are part of the government sent to deliver a nuke in Black Mesa. They also are assigned to eliminate Gordon Freeman along the way. They are extremely fast and have silenced pistols. Use the 9mm AR and just crouch down in a corner. They come from behind cover in the same spot everytime, so just plug them when they show themselves.

-Gargantua-
A huge monster that almost cannot be destroied by conventional means. Every time you meet one, you'll have to find some crafty way of overheating it, bombing it, or blowing it up. It can either stomp the ground to send a shockwave towards you or, when you get close, it can flamethrow you. It is surprisingly fast, too.

-Tentacle-
The only time where you will actully have to defeat these things is in the chapter "blast pit". You have to find some way cough-test-launching-the-rocket-cough that will kill it. The thing can hear you move, but not see. To navigate the blast pit, you much throw a grenade somewhere and let it go off. Once they start banging on the spot where it blew up, crouch and move towards your destination.

-Controller-
These are the brains in the Xeno outfit. They fly around and shoot energy balls at you. It takes a second for them to shoot, and at that time you should fire, then run. They aren't too smart, but their blast takes a toll on your health.

-Ichyosaurous-
I don't think i spelled that right. Anyway, this is the only water-based creature in the game. It is deadly though, as it is a Xeno form of Jaws. It is easily slain with a crossbow, and you can dodge it by strafing after it startes to charge.

-Gonarch-
This is the boss-before-the-boss thing. It doesn't attack you too much, but it can lay tiny eggs that hatch into baby headcrabs. It has lots of health and leads you on a chase throughout its lair. Watch the trees that are all around when you battle this thing. If you get too close to them, they snap down on you.

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