Mod More Betterer: L4D2’s Extended Mutation System

Your first mission: improve upon this somehow. Good luck.

My absolute favorite thing in the world is when games existences somehow mirror their names. Seriously. I have very few other interests. I’m an incredibly boring person. But anyway, just as Duke Nukem Forever took forever to come out, Call of Duty is nothing if not dutiful in its adherence to a yearly release schedule, and Toilet Tycoon was awful, Left 4 Dead 2 has not, in fact, been left for dead. Sure, Valve hasn’t lavished it with quite as much attention as, say, Team Fortress 2, but it’s certainly attempted to empower the community’s efforts – first with Cold Stream, and then with full Workshop support. But those mods? They’re about to get seventy five point blue banana apple sauce percent modderier, because Valve’s put its Extended Mutation System into beta.

Here’s how it works, via the Left 4 Dead zomboblog:

“What is EMS? It is vastly improved scripting system that allows script authors to go past modifying existing scripts and write custom script logic, spawn and control entities, and much much more. Mod authors will now be able to create deep custom experiences that can be played on any map or tailor create something for new or existing maps.”

In order to demonstrate, Valve’s included multiple new modes – including a spin on survival called Holdout – and other various examples that flex the toolset’s mighty scenario-morphing biceps.

A handy wiki, meanwhile, further explains the ins-and-outs of all of the above and also directing the Director. Unfortunately, it offers no advice on how to avoid the unsettling existential questions that you’re sure to encounter as a result. Basically, though, here’s the big takeaway: “The Extended Mutation System is now flexible enough to support the creation of Mutations that rival all-new game modes in complexity.”

Neato, huh? For now, though, the EMS is only just beginning to stir in its beta crypt, as Valve’s hoping to both squash bugs and add new features before releasing in full. Happily, in a gesture of (potentially prophetic) kindness, Craig put together this nice list of preexisting mods to tide you over. And hey, there are already velociraptors and lightsabers. The future of L4D2 modding is bright indeed.


  1. Meat Circus says:

    “Who directs the directors?”



  2. HadToLogin says:

    At least you can console yourself that L4D totally mirrors it name.

    • Meat Circus says:

      Not really, Left 4 Dead was entirely subsumed by its successor.

      • HadToLogin says:

        After some time, yes. But
        a) took’em long enough
        b) right after L4D2 release Valve completely forget about L4D1
        c) L4D2 made akimbo pistols useless (and inner John-Woo-Max-Payne hates that)

        I really wonder if Valve would put L4D1 in 2 if it weren’t for map tools and people already porting those maps. “They already done most of a work, let’s clean it a bit and score few points for being good-guy-valve”…

    • GameStunts says:

      All of the Left 4 Dead 1 campaigns are now in L4D2 aren’t they?

      It is a shame though. I love the gameplay of L4D2 with the melee weapons and additional infected, but I cared more about the characters in the first one.

      • Luringen says:

        The L4D1 campaigns are played with the L4D1 characters in L4D2.

  3. Askeladd says:

    Oh, this could be a chance for me to try out L4D2 again – maybe this time I’ll like it. After playing Killing Floor L4D is like a warm cup of water.

    • GameStunts says:

      The workshop has already breathed a whole new life into it. I got back into it when that happened, new skins for characters, maps and campaigns are really easy to install, it’s like playing the game when it was new. Nice to play a campaign that you haven’t rehearsed 100 times.

      • Askeladd says:

        A hundred times? I couldn’t stand 2 hours of that game. I’m just wondering if they archived some stronger blend of gameplay with the new mutation system. For example giving up the linearity, which L4D afaik always provided.

        • Luringen says:

          L4D was always linear, I don’t think it would work as an open-world game at all.

        • Premium User Badge

          phuzz says:

          There is a certain amount of alternate routes in some maps*, which are blocked/unblocked randomly on each play through, but apart from that it’s as linear as most other Source games.
          Personally I don’t find it a problem, but that’s just me.

          * for example in the campaign Wan Li the route can change quite a bit as routes are blocked off, which when you’re replaying a level it can be a bit of a surprise to run along the wall to find the previous entrance blocked off, forcing you to fight your way back though the horde to go around.

    • Xzi says:

      Killing Floor just feels like bite-sized Carnevil to me. Maybe it’s because so many of the maps are really small and narrow. In any case, it hasn’t tempted me to play save for the occasional Steam sale event.

      Is there any content that’s actually worth experiencing single-player?

      • Askeladd says:

        Oh, it’s really funny at certain parts. For example: Trapping the Patriarch behind the Doors on Biotics, repairing the Door faster then he is able to destroy it and throwing grenades in his face, through the little windows in the door.
        Also: I find the setting pretty amusing.

        Did you just edit, and ask if there’s something worthwhile in single player KF?
        It’s so much fun multiplayer. I can’t imagine playing it singleplayer.

  4. yurusei says:



    • Just Endless says:

      If you have to set up, and execute the full extent of the joke, it’s not a great joke.

  5. Spacewalk says:

    My speed reading comprehension was expecting expanded mutilation, being L4D and all, but I suppose that this will just have to do.

  6. Hoaxfish says:

    so, is there an Aliens mod for this?

    • mrwonko says:

      That’s a great idea and should be totally doable with these tools… A single more powerful special infected – probably a hunter – against a group of humans. There should probably be some common infected to help him out or it’d be too hard, or at least the humans need to achieve some goal which leaves them moving around so they can’t just hole up somewhere. Something like that.

      I came here hoping for inspiration I was not let down.

      • Gramarye says:

        Remove all the team helps, such as being able to see a pinned teammate through walls. Then all you need is some reason the team has to or wants to separate, and you’ve got the alien’s prey right there.

        • HadToLogin says:

          It’s called Realism + Boomer.

          That is, if survivors doesn’t use “disable boomered vision” mod.

        • subedii says:

          Yeah Realism mode basically removes those helpers. Coordination with your team mates become pretty important when someone can get jockeyed around a corner or off a drop and you have bright glowy outline to tell you where they are.

    • grundus says:

      There’s this link to and you can get the M41A elsewhere, so we’re already halfway there, all we need now is a map and some scripting. Can’t be that hard to outdo Colonic Marines so I imagine it’s just a matter of time.

    • pakoito says:

      There’s a great one for Killing Floor link to

  7. MikoSquiz says:

    So, any ETA on Team 4tress Dead? I want to kritz a pyro into a horde of zombies already.

    • godofdefeat says:

      There already are some TF2 server-side modifications which make the game into a TF2 version of TF2 (Zombie Fortress, Super Zombie Fortress etc.)

  8. CJ says:

    It occurs to me that a L4D2 mod that remodels and textures the survivors as Colonial Marines, and the various types of zombies as varieties of Alien would be on to a winner. You wouldn’t even need to mod zombie behaviour. I’d certainly map for it.

    It couldn’t be worse than the latest ham fisted attempt at the game.


  9. trjp says:

    For some reason I looked at the screenshot and wondered if one of the dinosaurs was not wearing shoes to fuel rumours that he was, in fact, dead!?

  10. nemryn says:

    L4D: Abbey Road?

  11. Slinkyboy says:

    Where’s my Split-Screen Co-op?? I wanna play custom maps with my joes at the house!