If the previous method didn't work for you for whatever reason, or let's say you have 1 controller, or maybe you wanna play a mutation or an add-on map then the second method should totally work for you.
If you have one controller
If you only have one controller to play with and you want the other player to use the keyboard/mouse you will need enable developer console. To do so go to option> keyboard > then check "enable developer console", once you do so you can press the tilde key [wiki.unvanquished.net] to activate the console. But, first things first, open a notepad from the start menu then copy and paste this code into it
name2 Player(2) ss_splitmode 2 //ss_enable 1 joystick 1 joy_advanced "1" // use advanced joystick options (allows for multiple axes) joy_name "L4D Xbox360 Joystick Configuration" joy_inverty2 0 joy_advaxisx 3 // x-axis controls GAME_AXIS_SIDE (strafing left and right) joy_advaxisy 1 // y-axis controls GAME_AXIS_FORWARD (move forward and back) joy_advaxisz 0 // z-axis is treated like a button joy_advaxisr 2 // r-axis controls GAME_AXIS_PITCH (look up and down) joy_advaxisu 4 // u-axis controls GAME_AXIS_YAW (look left and right) joy_advaxisv 0 // v-axis is unused joy_forwardsensitivity -1.0 // movement sensitivity joy_sidesensitivity 1.0 joy_forwardthreshold 0.1 // movement dead zone settings joy_sidethreshold 0.1 joy_pitchsensitivity 1.0 // look sensitivity joy_yawsensitivity -1.5 joy_pitchthreshold 0.1 // look dead zone settings joy_yawthreshold 0.0 joy_variable_frametime 1 joy_autoaimdampenrange 0.85 joy_autoaimdampen 0.5 joy_lowend 0.65 joy_lowmap 0.15 joy_accelscale 3.0 joy_accelmax 4.0 joy_response_move 5 joy_response_look 1 joy_autoaimdampen 0.3 joy_autoaimdampenrange 0.85 joyadvancedupdate // advanced joystick update allows for analog control of move and look // Alternate control 1 cmd1 bind "0" "slot10" cmd1 bind "1" "slot1" cmd1 bind "2" "slot2" cmd1 bind "3" "slot3" cmd1 bind "4" "slot4" cmd1 bind "5" "slot5" cmd1 bind "6" "slot6" cmd1 bind "7" "slot7" cmd1 bind "8" "slot8" cmd1 bind "9" "slot9" cmd1 bind "a" "+moveleft" cmd1 bind "c" "+voicerecord" cmd1 bind "d" "+moveright" cmd1 bind "e" "+use" cmd1 bind "f" "impulse 100" cmd1 bind "h" "motd" cmd1 bind "m" "chooseteam" cmd1 bind "q" "lastinv" cmd1 bind "r" "+reload" cmd1 bind "s" "+back" cmd1 bind "t" "impulse 201" cmd1 bind "u" "messagemode2" cmd1 bind "w" "+forward" cmd1 bind "x" "+mouse_menu QA" cmd1 bind "y" "messagemode" cmd1 bind "z" "+mouse_menu Orders" cmd1 bind "`" "toggleconsole" cmd1 bind "SPACE" "+jump" cmd1 bind "TAB" "+showscores" cmd1 bind "ESCAPE" "cancelselect" cmd1 bind "SHIFT" "+speed" cmd1 bind "CTRL" "+duck" cmd1 bind "F1" "Vote Yes" cmd1 bind "F2" "Vote No" cmd1 bind "F5" "jpeg" cmd1 bind "MOUSE1" "+attack" cmd1 bind "MOUSE2" "+attack2" cmd1 bind "MOUSE3" "+zoom" cmd1 bind "MWHEELUP" "invprev" cmd1 bind "MWHEELDOWN" "invnext" // controller2 bindings cmd2 +jlook // enable joystick look cmd2 bind "A_BUTTON" "+jump;+menuAccept" // (A) button - Jump -menuAccpt allows us to make selections on hud menus cmd2 bind "B_BUTTON" "+reload" // (B) button - Reload cmd2 bind "X_BUTTON" "+use" // (X) Use cmd2 bind "Y_BUTTON" "lastinv" // (Y) button - swap pistol/rifle or z_abort -used to respawn as a ghost. cmd2 bind "R_TRIGGER" "+attack" // RT - Main weapon - Primary trigger cmd2 bind "L_TRIGGER" "+attack2" // LT - Melee cmd2 bind "R_SHOULDER" "+lookspin" // RB - Fast 180 spin cmd2 bind "L_SHOULDER" "toggle_duck" // LB - Duck - is also used to give objects to people. cmd2 bind "STICK1" "vocalize smartlook" // LS - vocalize cmd2 bind "STICK2" "+zoom" // RS click - Rifle Zoom // Fixed bindings, do not change these across joystick presets cmd2 bind "BACK" "togglescores" // (back) button - scores cmd2 bind "START" "pause" // (start) button - pause cmd2 bind "S1_UP" "+menuUp" // Hud menu Up cmd2 bind "S1_DOWN" "+menuDown" // Hud menu Down cmd2 bind "UP" "impulse 100" // DPad Up - Toggle flashlight cmd2 bind "LEFT" "slot3" // DPad Left - grenade cmd2 bind "RIGHT" "slot4" // DPad Right - health cmd2 bind "DOWN" "slot5" // DPad Down - Pills sv_cheats 1 in_forceuser 1
Save the notepad file with any name you want (i chose split-screen.txt) into: Steam > steamapps > common > Left 4 Dead 2 > left4dead2 > cfg
Once you do that head over to your game and open developer console and type in:
exec split-screen.txt
NOTE: In my case, the name was split-screen.txt, depending on the name you chose you would exec the name of your txt file.
Then simply launch a split-screen session using the add-on from the previous section, you will be able to play with 1 controller and one keyboard/mouse combo.
If you want to play an add-on map
Unfortunately the previous add-on doesn't support launching add-on maps that aren't in the official list, to do so you will need the help of our friend Mr. developer console.
First you will need to know the name of the map you want to play, to do this simply launch a single-player game from the main menu with the add-on map you want to play, while in-game pause and then launch the developer console, in the top right corner there should be some text (You can move the console window away if it's blocking the text), the second line should say the exact name of the map right after "Map" and between the quotation marks, in this case it was the first chapter of Dead Center.
Just write the name down and you can quit the single-player session.
On the main menu launch the developer console and type in the following command
map "mapname"
Replacing "mapname" with the name of the add-on map you wrote down before, it would be something like this in our previous case:
map c1m1_hotel
Once you're in the game you will need to launch the split-screen session, to do so open the console again and simply type in:
connect_splitscreen localhost 2
Your game should re-load and you will be playing split-screen on your add-on map
If you're using 1 controller and keyboard/mouse you can also run the split-screen.txt script after executing the map.
NOTE: You can use this method for official maps if the split-screen add-on didn't work for you or you can't download it for some reason.
If you want to play mutations (or any game mode on add-on maps)
When you launch a map using the command
map "mapname"
It'll usually start the game in campaign mode, however if you want to play a game mode other than that you will need to type in the game mode name after the map name just like the following:
map "mapname" "mode"
An example of this if you want to play Versus on Dead Center's first chapter
map c1m1_hotel versus
Mutations work the same way but their names can be a bit tricky to find, you can click here [forums.alliedmods.net] to check out some names for a couple of mutations.
Once again, if you're using 1 controller and keyboard/mouse you can also run the split-screen.txt script after executing the map with your desired game mode.
connect_splitscreen localhost 2
You should now be playing in the game mode you want on any map you want, If you are playing with one controller and one keyboard/mouse use the trick in the beginning of this section.