http://mything.org/index.php?a=article- ... 0000000186
"Click the new game button as if you were going to make a new game. Have your Light vs. Dark game in mind as you set up the options in the first window.
Make the game time around 20 minutes or more as the LvD games can be somewhat long.
Make the difficulty level on "timid". This will balance the trrops out between Dark and Light forces. It makes for a more enjoyable game.
Hold down the right arrow key on your keyboard (the one next to the other three arrows, and is pointing to the right) and press the box that allows you to play the single player levels.
Continue pressing it and watch what happens. You should see the pregame screens acting funny. For instance your gimble on the wabe game has no info such as time, game type, unit trading or anything else other than a screen shot and the map name. Then you will notice that when a single player map pops up it will toggle back and forth from haveing no game info to haveing info such as difficulty level, time limit and unit tradeing enabled and so forth.
Try to stop it on a single player map with multiplayer map options listed.
Once you've done that simply select the single player map you want to play and hit ok. Heres the catch......your first game isn't going work.
You want to go ahead and start your game that you've just created and let it finish itself.
As soon as the game starts it will say "Game Over". Go ahead and restart(clicking leave game, and then creating a whole new game) the game without changing any options(this part is key, if you change any options whatsoever, even title, it will return to normal settings and you will have to start all over)
When you have all the players in the game go ahead and start her up! One team will end up with the light forces and the other with dark.(its done randomly so cross your fingers)
Some Co Op levels have a third party or "neutral" team. On co op's with cannons, there is a team that is with the cannons. They will not be able to play, as they have no units. Sometimes, like on "The Summoner" there are three teams that can actually play agianst eachother. On "The Summoner", a team can be either Light, Dark, or Spiders. I Highly recommend "The Summoner" to all of you, this is one of the best levels to do L vs D in. Also try Redemption and The Deciever."