They have also stated co-op will directly impact single player "giving players an alternative method of achieving ultimate victory." However they insist that this new gameplay is optional and alternative, and the whole single player experience can be fully done without it.
Finally, it was revealed that co-op will not feature existing characters, and that instead "players will create custom characters to fight on different and unique fronts in the war. This will include the ability to play as favorites like Turians, Krogans, Asari and more…each with their own unique set of abilities." These characters will level up and be able to upgrade weapons during the course of co-op play.
