Originally Posted by Kulmar

Advanced versus mode, endurance mod enabled (After ~10 swings, you swing like half the number of times)

That, along with the infected spawn bug comes from people getting creative with their server configs, there is no "mods" or "modes" out for the game other then the one that adds a tab for the server browser. The "endurance mod" and "infected spawning bug" along with increased infected distance they must spawn from survivors all comes from having sv_cheats 0 in the autoexec.cfg files. L4D isnt like CS or TF, you dont need to add that line to the autoexec.cfg on the server to ensure sv_cheats stay off.

As for what difficulty to set the game at for vs. mode, from my experience so far that comes down to what you feel entire campaign scores and duration should be at. I've done 3 scrims so far, one's score was 1869-1834 completed in 54 minutes on blood harvest another was 2436-1649 completed in 1 hour 14 minutes on no mercy with both being played at normal difficulty. Tanks/side were (not including the 3 tanks you get in the finale of course assuming how long it goes) 3/2 on blood harvest and 3/4 no mercy. On advanced we played 1 scrim on no mercy that ended up 867-659 that lasted 42 minutes which survivors only saw the safehouse on stage 1. The tank layout on that one was 2/2 with neither side lasting long enough in a finale for one of the automatic tank spawns to occur. I didn't track witch spawns as you can run right by her no matter where she spawns and not aggro her, it's the infected teams job to make sure you aggro her every time she spawns.