These will give you advice, open doors and if you are in a bad way give you health shots. Walk up to them and press action to get them to follow you.

This is the security of the Black Mesa Facility, they will help you kill any monsters around. Walk up to them and press action to get them to follow you.

These beasts will crawl slowly towards you before jumping at your face, just back off from them and take them down with 2 pistol shots. They first appear in Unforeseen Consequences.

These are created when a head crab infests a scientist. These slow moving creatures are rarely a threat. Just keep out of their long flailing arms. They first appear in Unforeseen Consequences.

These monsters appear to wear green slave collars as they are possibly controlled by some great overlord. The main risk they pose you is their green energy bolts they shoot. These will do significant damage so when you hear them charging it up duck behind the nearest pillar. Sometimes you can sneak up on them so keep an eye out for a dark arm protruding from behind an obstacle near by. They first appear in Unforeseen Consequences.

These monsters hang from the ceiling and lower their long tongues down to the ground. If you walk into its tongue it will pull you up and eat you. You can take them out with two pistol shots, avoid them or if the drop from the top is not too far let them carry you up and then kill them with a well aimed hit with the crowbar. They first appear in Unforeseen Consequences.

These enemies often appear in packs, causing more trouble than they will individually. These monsters first charge by closing their eye and shaking before emitting a high pitched sound wave in all directions. They only take a few shots to kill, keep above them or a reasonable distance away to take them out. They first appear in Unforeseen Consequences.

These monsters move only slowly but the green spit they throw towards you loses no potency with distance, luckily they are easy to hear and spot from a distance. They first appear in Unforeseen Consequences.

These highly trained members of the military is here to clean up the area, including any survivors. They will hide behind crates and are often very hard to kill. Keep behind any obstacles but don't let them get to close and watch out for grenades. They first appear in "We've Got Hostiles".

These cannot be killed with any conventional weapons and more often than not it is necessary to sneak past them. They are easily distracted with grenades. They detect your presence from sound so keep crouched while moving and don't shoot any weapons. They first appear in blast pit.

These terrifying monsters are some of the largest you will meet in the game and cannot be taken out with any conventional weaponry. They cannot fit down small corridors so you can often out run them. If you do get close they will fire on you out of their arms or stamp the ground sending out red plasma towards you. They first appear in Power Up.

These underwater monsters move at a great speed, one moment they are across the pool from you, the next you are being devoured. Sometimes you can take them out from the land with your hive arm but more often than not you can just out swim them. They first appear in Apprehension.

These are another part of the clean up operation. You only meet these fast moving women in a couple of places. They are very unpredictable and fast moving. Just hit them with what ever you can. They first appear in Apprehension.

Alien grunts quickly become one of the most frustrating enemies. Your first warning of their presence will be the sound of their loud clumping footsteps running around below you. Their weapon is the equivalent of the hive hand weapon you will pick up later in the game although they can also destroy you will devastating blows from their arms. If you have a height advantage, there is a door between you or you are in a space they cannot fit in then keep out of their sight and use your hive arm to take them down, or use another weapon and flee when the small bugs come after you. If you don't have the time or space for this method a some energy from the Gauss Gun will destroy them, charging it to around 11 can take them out in one shot. If you are really having trouble then explosives can be used to take them out, but beware a bad shot with the rocket launcher can fail to take them out so save before trying it. They first appear in Questionable Ethics.

These small enemies chase after then nearest living creature and then explode, the best method for dealing with them is to run away until they explode of their own accord. Eventually you will be able to use them as a weapon but beware if there are no other enemies about they will turn on you. They first appear in Questionable Ethics.

These fast moving creatures only appear once you reach Xen. They shoot yellow energy balls at you, these often come in groups, just keep moving. They hive hand is very effective against these enemies, taking them out even when you cannot see them.

This monster has a whole level named after her (Gonarch's Lair), as this is how long she takes to kill. She produces baby head crabs and also shoots radioactive waste at you. Her hard shell is impenetrable, so shoot the sack hanging down below her.

These little monsters only appear in Gonarch's Lair, they are smaller than normal head crabs so harder to hit but the same method can be used to destroy them.

This is the final boss, destroy his power crystals before destroying him.

This mysterious character appears all through the game, the monsters do not appear to attack him and he seems totally in control of the situation.

Your first sighting as you enter the Black Mesa Complex.

G-man arguing with a scientist near the start of the game.

G-man talking to you at the end of the game.