Mass Effect 3 is getting a free a multiplayer expansion pack, BioWare has announced.

The biggest Mass Effect 3 expansion yet, Retaliation sees the return of the Collectors as a new enemy in multiplayer matches.

Players will do battle with the Collector Praetorian, Scion, Abomination, Trooper, and Captain, as well as Cerberus Dragoons and Geth Drones.

New character kits will be available including the Turian Havoc Soldier and Turian Ghost Infiltrator, with more being added on a regular basis, said BioWare.

Six new versions of existing maps are also included, which feature new environmental hazards and traps.

New weapons and upgrades added include the Collector assault rifle, sub-machine gun, and sniper rifle, and some new ammo modifications and unique pieces of equipment will also feature.

A new reward system has also been added, doling out Challenge Points when various multiplayer assignments are completed. These points may be used to unlock titles and banners to display in-game.

Mass Effect 3: Retaliation is due on or near October 10.