No zombie will live along as one of us still breathes.

So there’s been some guys working on these mutations... turns out there is more than 1 Survival Mutation after all, which we all know the one is Versus Survival.

The other survival mutations are:
Classic Survival
Hordes
Jimmy Gibbs Only!
Nightmare
and Realism Survival

I tested each of these on the bridge...

Classic survival is basically L4D's version of survival. Only Smokers, Boomers, Hunters, tank, and common infected spawn. You only get weapons that are in L4D as well, so no melee weapons here.

Hordes is my least favorite, it’s actually very boring. Nothing but horde spawn. No SI, no Tanks, just common infected.

Jimmy Gibbs Only! is nothing but hordes of Jimmy Gibbs spawning. No Tanks or SI. This one I actually lasted 27 mins alone (the bots died within 3 minutes lol) and I moved around from corner to corner only meleeing which is very effective against the Gibbs.

Nightmare is my favorite version. This one has no common infected, but loads of SI and Tanks. Plus, no survival glows, and its foggy has hell. Fire is very effective here. I lasted 17 mins with the bots, not too bad I think.

Realism Versus you can pretty much guess works the same as the other realism game modes. No survival glows, so all you have is good teamwork!

There are loads of other mutations for all the other game modes, which I haven't checked out yet, but this is definitely worth downloading.

This addon(well, there are actually 2 of them) adds selections in the main menu just like how Realism Versus' for example was added, so you can easily navigate to the game mode you want to play! I think that is a huge bonus, so you don't have to type commands or anything like that.

You can download it here, it seems to be updated every week so thats something to note down that this has to be updated everytime L4D2 updates.
http://forums.steampowered.com/forums/showthread.php?t=1529433&highlight=custom+mutation