Co-op is a feature not commonly found in RPG's, so this is big news for the franchise. Co-op mode is unlocked just like battling as evil: you must get to a certain part in the game. Once it's unlocked, you can turn it on and off at any point in time. Here's all the details in a nice list:
Can be switched on or off on the fly in adventure mode--you do not need to load a special version of the game. Simply go into the menu at any time and select Co-Op (the last option). You will also not be penalized at all for playing in Co-Op mode.--there is no 'lesser ending' or anything like that.
Player 1 controls: Berethor, Elegost, Morwen Player 2 controls: Hadhod, Idrial, Eaoden
The player who controls adventure mode and the menus is the player who controls the character on screen. For Example, if Idrial is on screen in adventure mode, then Player 2 will only be able to walk around in Adventure mode and go into the menu system. This can be changed by simply swapping Idrial for a player 1 character (Berethor, Elegost, Morwen)
When guest stars appear in your battle such as Gandalf, control of that guest star alternates between player 1 and player 2.
We've received a number of emails from people asking how to enable co-op mode, and to be completely honest this stumped us for a while too. Enabling it, however, is not hard. All you have to do is plug in a second controller, and the option will become available.