Surviving the L4D Survival Pack

[quote=Steam] Survival Mode pits your team against never ending waves of infected. Sounds simple. Just trap the survivors in a small part of a map, unleash the hordes, and record the longest time. Survival Mode, which will be released next week, is actually a bit more than that.



Our goals for Survival Mode are to deliver a mode of play distinct from Campaign or Versus, have games that regularly last under ten minutes, and emphasize competition with team play through leaderboards.



Survival Mode draws on the planning and communication aspects of a successful Finale or Crescendo event, while taking it to another level. It rapidly hits a fever pitch that only a well coordinated team will be able to successfully survive. Everything from simply covering a reviving teammate, to making every shot count to minimize reloads becomes crucial in Survival Mode.



Given the importance of pacing in Survival Mode, we need to define as precisely as possible how the difficulty ramps up during the course of a round. We have numerous variables to work with: mob spawn frequency, special infected spawn frequency, number of each type of special infected, total number of special infected, tank spawn frequency, total number of tanks, and so on. We need all of these variables to work together to create a fairly smooth difficulty curve.



If the curve ramps up too sharply, we find that teams of all skill levels tend to hit a wall at the same time. There isn't enough variation in the times to separate great teams from average ones. If the curve is too flat, then average teams will have a good experience, but really good teams can grind on long enough to cross the line from having fun to just getting worn out.



It might seem that just gradually increasing spawn rates and numbers of infected will create a nice smooth curve, but it turns out to be much trickier than that. Each type of infected has its own spawn schedule, so even though the individual spawn curves may be designed to be fairly easy at a particular point in time, sometimes they overlap in just such a way that the players find themselves in a really bad situation far earlier than we intend.



For example, a tank will be much harder to fight if a mob of common infected spawns at the same time - and nearly impossible if three hunters also show up right at that moment. A similar situation can happen due to variables outside our control - a team may not dispatch a tank or mob quickly enough, causing subsequent waves to start arriving and piling on to an already difficult battle. It's also hard to anticipate when teams will need to make an ammo run or heal up, both of which can be extremely difficult only a few minutes into the round. In order to help visualize these overlap points and the collapse of each spawn curve, we graphed out the wave behavior of infected over the course of a survival round.



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