Part 16

Collect the ammo canister near the spiky plant.

Jump back across to the ground left of the whoosh-thing, avoiding the whoosh-thing itself.

Equip the shotgun and run up the curving pathway.

Be ready to double-barrel a vortigaunt that teleports in ahead.

Get the health pack and ammo canister from near the dead HEV suit wearer.

Quicksave (save your game at a checkpoint (an auto-save point you restart from on death)) and move into the second part of the headcrab tunnel.

Proceed cautiously with the pistol or assault rifle out to shoot headcrabs.

After encountering one headcrab, section ba_xen6 will load.

Continue cautiously down the tunnel, encountering three more headcrabs before a drop-down point.

Equip the shotgun, turn on your flashlight, and quicksave.

Drop down and turn right to find a large rock to hide behind as two vortigaunts teleport in ahead.

Wait until the first vortigaunt is in shotgun range, then blast it.

Let the other vortigaunt see you.

Quicksave and run outside.

Double-barrel the vortigaunt that teleports in on the walkway near you.

Immediately turn and jump into the teleporter orb that Dr. Rosenberg's voice is coming from.

If fast enough, you will make it before a nearby alien grunt can hit you with any of its hornets (small projectiles).

You will end up back in the lab in section ba_teleport2.

After appearing in the teleporter lab, listen to Dr. Rosenberg and follow him to a lift.

Get on the lift and quicksave before using its button panel.

There is a small chance the game will glitch and not load the "Power Struggle" chapter as you descend; if this happens, quickrestore (load your last save) and try again.

After the lift stops, use the button panel to the right of the large door to open it.

Stay near the button panel and use the pistol to sneak-shoot the bullsquid just past the door.

Check near the dead guard for bullet ammo and armor items.

Get on the lift past the guard and use its button panel to go up to a higher floor.

Go down the hall past the lift to where you can look through a fence and see a guard and a scientist discussing the power cell the lab needs.

After they are killed by a vortigaunt, go back down the lift (or drop down) and get out the .357 Magnum.

Marines will soon start cutting through the "RESERVE COOLANT BASIN" door.

Stand in the big doorway near the lab's lift so you can only see the right half of the door they are cutting.

Quicksave when the door is almost cut open, then wait until it falls.

As soon as it falls, shoot one of the explosive containers just past the right edge of the doorway.

If done fast enough, both marines will be killed. If one survives, either sneak-shoot him or quickrestore and try again.

There are supplies in the room past the cut-open door.

In the area past the big doorway on the right are three marines who are impossible to sneak up on or sneak-shoot.

After quicksaving, let them see you, then run back to the lab lift's big doorway and stand so you can see part of the cut-open doorway.

Have the assault rifle out and use AR grenades to kill marines as soon as they appear in the cut-open doorway.

Alternatively, let them see you, run back to the lab's lift, and use it to return to the previous section.

If any marines see you as you descend in the lift, quickrestore and try again.

Quicksave once you make it back down unseen, then crouch-walk slowly to see where the marines are.

You should be able to sneak-shoot at least some of them, aiming for the head with .357 slugs for one-shot kills.

If you cannot get them all without being seen, use the lab's lift again.

If you have snarks from Chumtoad's Lair, go up near the doorway to the marines' area without being seen, then toss three or so snarks toward the doorway.

Immediately run back to the lift room and wait for the snarks to explode.

Run into the doorway and toss a couple more snarks toward surviving marines.

They will see you, so quickly retreat to the lift room.

If snarks don't finish them, toss more from the lift room's doorway, or ride the lift up and back down before more snarking or sneak-shooting.

Once all three marines are dealt with, go to the room past the cut-open door and look for health packs and ammo, including two RPG rockets and a C4 satchel bomb.

Past that, go through a fence doorway to a room with a power meter, then go through its other doorway.

Turn right and go through another doorway, then crouch-walk up to the big window on the right.

Get to where you can see part of a marine through the right side of the window, then carefully sneak to take him down with one headshot (a shot that lands on the enemy's head, usually an instant kill) from the .357.

After he is down, bash the small boxes nearby to find two health packs.

A nearby marine will shout "Movement!" when you go through the doorway to the blue-lit room, but he has not really seen you.

Bash the boxes in that room for another health pack.

Crouch-walk up to the right side of its other doorway.

The marine is over to the left, so edge carefully to where you can use the .357 to perform a sneaky headshot.