Looks like it's about time to dive back into Valve's zombie apocalypse/gnome rescue/friendly fire simulator, Left 4 Dead 2. An update announced on the Left 4 Dead blog has added a finished version of the community made map, Cold Stream, and has opened up all mutations. These are custom rulesets created by Valve and the community which used to rotate every week or so that operate as tense and often ridiculous alternative game modes. Highlights include Taaannnkkk! which replaces all special infected in versus with Tanks, and Last Gnome on Earth, which requires survivors to rescue and protect Gnome Chompski on every map.

A bunch of tweaks have been made to Crash Course, Death Toll, Dead Air and Blood Harvest to crush exploits, and to celebrate the entire ordeal, Left 4 Dead 2 is on sale on Steam at 75% off. Absorb the latest round of tweaks in the patch notes below, and browse the many available mutations archived over on the Left 4 Dead wiki.

Patch notes, via Steam:

Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

- Made all mutations accessible from the main menu

CRASH COURSE

Crash Course 1:
- Fixed survivors being able to climb into infected-only territory from the top of the white truck in the early alley.
- Survivors can no longer leave the map bounds near the riverfront.
- Closed off a shortcut method to bypass the howitzer event.

Crash Course 2:
- Survivors can no longer jump on the generators in the finale area.

DEATH TOLL

Death Toll 1:
- Moved car near the tunnel entrance away from the drooping traffic light, as standing on parts of the car near the traffic signal could put you into a permanently stuck position.
- Moved a traffic sign that allowed survivors to climb the drooping traffic light prop up to the top of the tunnel entrance.

Death Toll 2:
- Added an infected ladder leading in to the upper pipe in the large drain room.
- Survivors should no longer be able to cross the bridge-lowering event before the bridge has fully lowered.
- Survivors should no longer be able to access the infected-only areas toward the end of the level.
- Survivors should no longer be able to leave the playable areas of the map from the areas beyond the saferoom.

Death Toll 3:
- Added "Checkpoint" flag to the nav square at the end of the intro saferoom to prevent versus rounds from starting when survivors stand next to the door.
- Removed a nav square by the next-level saferoom door to prevent infected players from standing there to prevent the round ending.
- Tweaked saferoom level transition trigger brushes to prevent infected players outside of the saferoom preventing the transition.

Death Toll 4:
- Players can no longer access the right-hand corner just outside the starting saferoom. This is to address a permanent-stuck spot when the saferoom door is opened.
- Survivors can no longer climb over the van in the ally leading to the onslaught area, which allowed them to skip most of the level.
- Survivors should no longer be able to leave the map/enter infected-only areas outside of the onslaught even street.

Death Toll 5:
- Made the roof of the picnic area inaccessible to survivors. This resolves an invincible spot.
- Players can no longer jump on the electric box prop facing the water on the side of the lakehouse.

DEAD AIR

Dead Air 1:
- Moved a bookshelf in front of the window in the second interior area (before the ladder climb) to prevent players from skipping parts of the level.

Dead Air 2:
- Move the trailer below the office building out of jumping range to prevent players skipping the offices.

Dead Air 3:
- Moved the fence and fence-climbing props at the entrance to the construction yard further back into the alleyway.
- Several tweaks to the area near the construction yard to prevent survivors from setting off the barricade fire event before they enter the event arena.
- Boarded up a window in the construction yard to address survivors accessing an invincible area.
- Survivors should no longer be able to jump over the barricade.

Dead Air 4:
- Infected players should no longer get stuck climbing over the rubble that divides the start of the map from the balcony leading to the escalator side .
Dead Air 5:
- Fixed a visual bug caused by a cube map being hidden inside of a prop.

BLOOD HARVEST

Blood Harvest 1:
- Survivors should no longer be able to leave the map by jumping to the left toward the end of the rope bridge..

Blood Harvest 2:
- It is no longer possible for survivors to climb in the vent above the alarm room.
- Survivors can no longer stand on the horizontal pipes under the catwalk in the area following the alarm door event.
- The high pipes along the sides of the train tunnel are no longer accessible to survivors.

Blood Harvest 4:
- The roof of the starting safe room is no longer accessible to survivors..
- Survivors can no longer jump on top of the “Richardson Atlantic” building.

Blood Harvest 5:
-Removed some of the crossbeams in the hay storage building.

COLD STREAM

Cold Stream 1:
- AI infected can now access the roof of the watchtower.
- Survivors can no longer jump on top of the roof of the single-storey cabin at the far end of the area after the rope bridge.

Cold Stream 2:
- It should no longer be possible for survivors to jump up to the top of the tunnel entrance pipe near the start of the map.
- Survivors should no longer be able to jump over the fence on the bridge toward the end, skipping the barrel explosion event.
- Changed the M60 spawns into weapon_item_spawn to be more mutation friendly.

Cold Stream 3:
- The walls toward the back of the bridge (opposite of the direction players go to progress the level) are no longer accessible to survivors. This is to prevent survivors from getting into infected-only areas below the bridge, which they may not be able to escape from.
- Changed the M60 spawns into weapon_item_spawn to be more mutation friendly.

Cold Stream 4:
- Hooked up a quick conversation between the chopper pilot and the triggering survivor.

A new official blog called Valve Linux has popped up, put together by an 11-strong team of developers on a mission to "strengthen the gaming scene on Linux, both for players and developers. This includes Linux ports of Steam and Valve games, as well as partner games. We are also investigating open source initiatives that could benefit the community and game developers."

The team was set up last year, and have been experimenting with porting Steam and Left 4 Dead 2 over to popular Linux operating system, Ubuntu. "We’re just starting development and working with a single distribution is critical when you are experimenting, as we are. It reduces the variability of the testing space and makes early iteration easier and faster," say Valve.

That's just the beginning, however. "Based on the success of our efforts around Ubuntu, we will look at supporting other distributions in the future." They've got Left 4 Dead 2 running natively on Ubuntu, and a basic version of Steam. They're planning to polish both up over the course of the next few months and look into porting more games onto open source platforms.

"We’ll be posting more information about those projects (and others) on a regular basis. Since this is a new effort for the team, we’d love to hear your opinions about the blog so shoot us an email. We also encourage you to leave comments and ideas for future postings. We want this to be a community of game developers, communicating with each other and talking about current efforts and future efforts in a powerfully creative environment."

You can take part and let your view be known over on the Valve Linux site.

You love Steam sales. I love Steam sales. EA, however, don't love Steam sales. Just a few weeks ago their senior vice president made his opinion clear, claiming that they "cheapen" intellectual property. A few days ago the Origin Summer Sale kicked off anyway.

We asked Valve's director of business management, Jason Holtman, whether Steam sales have any affect on day-one purchases during last week's Develop conference. He doesn't agree with EA. Not even a little bit.

"If that’s what we thought was happening, or that’s what we saw happening, we wouldn't do it. Actually, all the data is contrary to that. A promotion is not a policy; a promotion is just a feature to give people more value," said Jason, speaking to PC Gamer.

"It’s not as if a 75% offer or a 50% off sale at some point in time cannibalises a sale that would have happened earlier, it’s just not true. We’re actually seeing both of them growing. We don’t see one cannibalising the other. If we did, we wouldn't do it." he continued.

Steam sales go from the sublime to the ridiculous-ly cheap. There's even one going on right now. Check out this real time evidence of a Steam summer sale in progress. It's a wonderful time for bargains.

"We put Left 4 Dead 2 and Portal 2 on sale. If we thought that was killing our franchise, or hurting the value of games, or hurting the revenue we could generate as a company, we wouldn't do it," continues Jason. "We've even gone so far as to give away Portal for free a couple of times. Whole days where it's not free for a day, it's just free."

Valve's sales still weren't dented: "We looked at this amazing data afterwards. The day after the sales were exactly the same, if not more," he says.

"People aren't making a decision thinking 'I'm always going to wait for perfect pricing.' There are time elements to it, there are fan elements to it, there are value elements to it. People sometimes like paying the full amount on the first day because they want to play it now and they want to be a fan.

"Those features you’re talking about - like the sales - we just think of them as customer features. They're not policies or mandates. Things like this are super smart: this would be fun; people would play this game; they’d pick it up if they didn’t have it; they’d tell their friends about it."

For more from Jason, check our story on how TF2 inspired Greenlight. We've also posted his views on Greenlight's rating system.

Thanks to Dan Griliopoulos for the image.

VG247 are reporting that Valve have finally announced a release date for Left 4 Dead 2's Cold Stream campaign. Now I know what you're thinking, you're thinking "But Tom! Isn't that campaign out already?" To which I reply "How can I hear what you're thinking, am I telepathic now?" But also "Nope, it's just been in beta testing. For a year." Which is a fairly speedy release in Valve time.

Cold Steam has spent the last year in community testing, with Valve gathering data on how the players perform on the map and adjusting it accordingly. But it's technically never been released until now, or rather until July 24th.

Assuming other Valve projects follow this release pattern, we estimate we'll be able to review Dota 2 sometime around 2014. In fact the truth is Half Life: Episode 3 was actually finished in 2009, but Valve feel it needs another six years of testing to be sure they got it right.*

*Probably not the truth.

Shortly after Payday devs, Overkill, announced that they were working on something with Valve, rumours began to pop up suggesting that that something could be a prequel to Left 4 Dead. That might sound like a promising idea, but it isn't happening. Valve developer Chet Faliszek put a swift "woah, nelly!" on those rumours in a chat with PCGamesN.

"I want to make sure that people don't think the prequel is coming," said Faliszeck. "If that happens, then it will make this other thing we're doing feel uncool, when the thing we're doing is really cool."

Chet described Valve and Overkill's new thing as "kind of akin to how in TF2 you might see some other games' weapons get translated and put into that game."

"We're doing something similar to that, but it's a little bit more involved," he explained.

A character crossover perhaps? Criminal clown masks for Left 4 Dead survivors? Tanks in cop hats? Valve are being discreet. "We're trying to be a little coy and a little fun because we want the communities to discover it," said Chet, "but those guys are still making Payday: The Heist, we're still making Left 4 Dead."

We'd previously heard that Payday: The Heist developers Overkill are working on a game with Valve, but details were scant - all we knew is that it was Left 4 Dead related. Our megapals over at CVG cite a source as saying that it's going to be a Left 4 Dead prequel which details the genesis of the zombie uprising.

"As perceptive gamers will have noticed, several hints have recently been dropped into Payday: The Heist, which has led to various rumors," the original statement from Overkill read. "We are excited to be able to confirm that an in-depth collaboration between Overkill and Valve is currently in production. We are working on a very cool blend of Payday and Left 4 Dead."

It's a really nice idea for a collaboration. In Left 4 Dead you're the good guys. In Payday, you're the bad guys. Combining of the two, you could be a bunch of morally grey guys. Also, it's a prequel, and everyone loves prequels, right? If not, don't worry: Overkill are also working on a sequel to Payday: The Heist.

In many ways, Payday: The Heist is very similar to Left 4 Dead. You team up with three friends, you fend off hordes of enemies and try to stay alive. But, in a few important ways, they're very different. In Left 4 Dead, a throng of zombies are trying to keep you out of a safe room, in Payday, you rob banks, take hostages and mow down legions of cops. According to a post on the Overkill blog, spotted by VG247, the Payday devs are working with Valve on a collaboration that will bring both concepts together.

"We are excited to be able to confirm that an in-depth collaboration between OVERKILL and Valve is currently in production." says Overkill director Ulf Andersson. "We are working on a very cool blend of PAYDAY and Left 4 Dead."

A "cool blend," eh. Time to indiscriminately mash Left 4 Dead and Payday's premises together until something works. Zombies robbing a bank? Survivors robbing a zombie bank? Tanks robbing a bank? Crims robbing a bank staffed by Tanks? This isn't working. What do you think it'll be?

We've seen some impressive fan-made Portal guns in the past, but they've been rare, costly one-off projects. Valve are giving us the chance to get hold of our own Aperture Science Handheld Portal Devices without having to burn ourselves horribly putting together an injection mould. Joystiq mention that, at Valve's request, toy manufacturers, NECA have put together a life-sized Portal gun. It'll hit the shops this summer with a $130 price tag attached.

There will be lights and those lights will change colour, but will it make the "pwung" noise? There's only one way to find out, and that's to buy at least five. Perhaps ten. Maybe more. More. MORE.

NECA will also be releasing a line of Left 4 Dead, Team Fortress 2 and Half-Life action figures, a few of which were shown off at the NYC Toy Fair. The Team Fortress 2 wiki has a snap of the new figures, you'll find that below along with a few shots of that Portal gun. Baggsy the Heavy.

This is the full length version of the Left 4 Dead fan film that was teased two weeks ago. With Bill's tragic demise, the Left 4 Dead crew are a member short. On the way to a safe room three blocks away they find a replacement. And then another one. And then another, until everything's gone a bit mad. Which one would you pick to become the crew's new fourth member?

http://www.youtube.com/watch?v=vBamb_bBhbo

Of the pile of custom L4D2 campaigns I've played, Questionable Ethics has stuck with me most. It's filled with surprise; a white-walled gauntlet of mystery and torture that you must, must, must download. I introduced Tyler and Chris to the four-stage campaign, then we sat down to talk about it.