In our last batch of first hands-on impressions with Valve and Turtle Rock's cooperative zombie shooter Left 4 Dead, fellow Shacknews editor Chris Faylor and I were introduced to thousands of bloodthirsty new friends. Returning to Valve's offices last week to play the latest build of the game, I finally met the belle of the ball: the witch.

When you first encounter her, Left 4 Dead's fifth and unplayable boss infected is a peculiar sight. The notion of a plainly-dressed and raven-haired young woman sitting in the middle of an urban sidewalk might even be plausible, had the city not been teeming with the hungry dead. But perhaps most unsettling is the quiet weeping; the witch is most often heard before she's seen.

I turned to Valve writer Chet Faliszek, my guide through the latest build of the game. "Even if we're going to die," I asked, "Can I request we take her on anyway?"

Faliszek agreed, perhaps with a bit of trepidation. Even with the witch's inclusion in the game's normal difficulty—previously seen only in hard mode and above—she's no pushover, and the game goes to great lengths to make you aware of the danger she presents. Your companions' spoken dialogue, procedurally prompted by the events unfolding around you, warns you to move quietly and turn off the flashlights. There's a friggin' witch around here somewhere.

"The witch will definitely kill somebody," explained Faliszek. "She's entirely lethal. Whoever sets her off, she'll go after that one person and she will kill them. Other creatures, yeah, you can push them away, you can run, you can do all these different things, but she is single-track. She's going to kill you."

We readied our shotguns and our wits as Chet tossed a Molotov cocktail, setting the witch and her surroundings both ablaze. Immediately we all opened fire, desperate to put her down before she could retaliate, and we were met with success. The tension passed.

Since Faylor and I played the game last January, Left 4 Dead has been more or less completed and is now moving into the test and polish phase of production. The most current build shows marked improvements in lighting and environmental audio, as well as the sort of tweaks that make for a more visceral experience.

But most notable among the changes are the inclusion of so-called "crescendo" events, scenes in most stages that require you to bunker down and defend against large-scale waves of zombies while waiting for some time-sensitive mechanic to complete before you can move on.

"They're essentially mini-finales," Faliszek explained. "But we hate to use the word 'mini'."

During our play of a single scenario, the previously-seen urban stage, we encountered one of these new crescendo events outside of a warehouse, where we had to wait for the slow descent of a elevator down a scaffold before we could continue. Chet hit the switch, and the horde soon followed. The anchored miniguns and sandbag defensive locations made for an obvious last stand locale, but we wouldn't have survived without a bit of strategy.

The addition of the crescendo events—which will appear in most of each scenario's five stages—came about as a result of Valve's trademark extensive testing, in which playtesters told the company that they enjoyed planning and staging assaults with their comrades. Another crescendo event, described but not yet implemented, was an instance in which players must fend off the infected inside of a slowly ascending and fully destructible freight elevator, accompanied by a slow-ticking floor indicator to amp up the tension.

"The feedback from players was always that they liked the testy moments. The ability to set up and look at the situation. So much of the game is on the run, your strategies have to really flow," Faliszek noted.

Turn the page for more on Left 4 Dead's Director AI, and Chet Faliszek's noble sacrifice of a fellow Valve staffer in the name of games journalism.