[Necromancer]

Urban Flight

Surfacing

After the elevator reaches its top floor, exit it and twist the wheel nearby to open a small supply room. Buried under the rubble here is another orange crank, so grab it and bring it back down towards Alyx and fit it into the socket on the wall. Doing so will let you twist it again and open up the path leading upwards.

When you’re finally up and on the surface, feel free to listen to Dr. Kleiner for a while; he’s got a long list of stuff to talk about. Be sure that Alyx is listening when he starts talking about procreation; she really needs to get the point of that, if you know what we mean. Yeah, baby.

Use your gravgun to clear the path leading on, and watch for Combine troopers that’ll start to rappel in from the rooftops. There’s a cinderblock in a milk crate near here, so use it to blast your enemies right in the face, then grab their SMGs. Finally, something a bit more hardy to fight with...there are more Combine soldiers up ahead, along with three antlion burrows. You know what to do with these things.

At the end of the street with the burrows, find the barred door and destroy the wooden bars over it. Inside, a pair of Combine troopers will be attempting to place mines on the walls. Do your best to show them the error of their ways by shooting one of the mines. This’ll kill the troopers, but will also unfortunately set the whole hallway on fire. It’ll be up to you to find the propane tank that’s feeding the fire and shut it down. Doing so is a simple matter of walking around the corner here. Unfortunately, the tank is on a ledge that’s too high to reach, forcing you to walk along a precariously balanced pipe to get to it. Just before you jump, it’ll fall down, though.

The solution here is simple but non-obvious. This doesn't have to be a physics-based puzzle; there may not be enough objects in the area to let you make a counterweight for the pipe and prevent it from falling. Instead, walk along the pipe until it falls down, then zap it with your gravgun’s primary fire, which will cause it to rise up momentarily. Use this moment of opportunity to jump across the gap and reach the far side, then quickly turn off the gas so you and Alyx can proceed upstairs. If you want to try a more secure method of making the jump, you may be able to form a counterweight by placing every single object in the area on the rear end of the pipe, or you can wedge it into place by shoving a rock between the pipe and the ground near it, preventing it from rising.

Using The Enemy’s Tools

After fighting your way past the zombies in the upper floor here, grab the rollermine that’s attempting to zap you and let Alyx convert it to a friendly. With that done, head down the steps, watching out for sniper fire, and do your best to grab the second rollermine and convert that as well. When that’s done, shoot them both out into the street beyond the doorway; the sniper will think of them as targets and attempt to fire at them, giving you a perfect opportunity to dash out and take cover behind the cars. When you’re close enough to the sniper to do so, grab a rollermine and chuck it into the window he’s hiding in; moments later you’ll be treated to a glorious display of ragdoll death.

At this point, Alyx will proceed upwards and take over the sniper rifle to cover your advance down the street. After jumping off of the platform she opens up for you, avoid the zombies until you can head into the nearby building, but watch out for the toxic headcrab lying in wait for you. When you reach the elevated walkway, blast the planks off of the windows with your gravgun to allow Alyx a better shot at the zombies that come at you. When you hit the street again, push the car nearby into the antlion pit, but not before you remove the piece of metal that’s obscuring the Combine soldier from Alyx’s shots.

When the far barricade opens up to issue forth some troops, wait to one side for Alyx to take a couple of them down, then dash inside and finish off any remainders with your shotgun. At this point, Alyx will begin following you, so get atop the barricade and cover her approach with whatever weapons you have available.