I have some interesting ideas for new factions that can be introduced in Mass Effect 3.
Cerberus Veterans(working name)-Basically these are the Cerberus loyalists(no implants) These are not the abducted test subjects that get turned into the members of the current Cerberus faction we have. They are fully human. Armor is similar to the first Mass Effect. In addition, Mechs will be featured.
Armor:Freedom Armor w/Armor Weapon:M-22 Eviscerator, M-96 Auto (white with yellow trim and is fully automatic) and M-30 Titan (black with chrome trim. Based on original ME1 sniper rifle design) The commando is unique in the sense that it has the ability to switch back and forth between 2 weapons to correspond to long range and short range attacks respectively. Power:Uses flashbang grenades, singularity and deploys shield generators.
Armor:Freedom Armor w/Shields Weapon:M-29 Incisor Advanced (black with yellow and orange trim. shot causes lingering damage for 5 seconds Power:Tactical Cloak
Armor:Hoplite Armor w/Shields Weapon:M-7 Gorgon (black version w/chrome trim of M-8 Avenger. Features polonium rounds. Opponents die very similarly to the way chemical and radioactive round worked in ME1) Power:Grad Turret(Medium sized floating turret with dual barrels. Fires green laser round similar to Geth weaponry)
Heavy Soldier Male
Armor:Cerberus Assault Armor w/shields Weapon:Arc Projector
Weapon:M-10 Harpy Pistol (black version w/chrome trim of M-3 Predator.)
Weapons:Gatling Gun and Rocket Launcher
Weapon:M-12 Hydra Shotgun (black with chrome trim. Based on original ME1 shotgun design)
Ogre Mech(arms can be blown off)
Weapons: M-333 Beam(Center eye. If destroyed, ogre loses control and randomly attacks in all directions, friend or foe), Storm(right arm. similar to the blackstorms attack but red in color), and Leash(left arm. green in color. similar to the wave beam from metroid prime) Does continuous damage as long as the attack is hitting you. If your health hits zero, the mech will lift you in the air and toss you.
A second Geth Faction (I don't know what else to call it)
Geth Recon Drone
Weapons:Mounted pulse gun Powers:Tactical Cloak
Weapons-Laser Sight Sniper
Geth Destroyer (Green with orange trim)
Weapon:M-100 Grenade Launcher Power:Incinerate
Geth Juggernaut (Gray with Red trim and Red light)
Weapon:Geth Spitfire Power:Overload
Geth Shock Trooper (All white)
Weapon:Arc Pistol Power:Cryo Blast, Hexagon Shield
Weapon: Main cannon and Missiles
Geth Sniper(Brown with orange trim)
Weapon:Javelin Power:Defense Drone
The second Reaper Faction (No names for all the enemies right now)
Hanar Husk (Pariah)
Powers:Salvo(biotic attacks launch from all tentacles simultaneously and close in on your position) When close, it will swing at you with its tentacles. WARNING:If you get too close, it'll pick you up off the ground with a tentacle and proceed to stab you repeatedly with the rest for an instant kill.
Weapons:Turret located where the Elcor's mouth would normally be.Reaper Blackstar mounted on back.(will use when you are at a significant distance)
Powers: Enhanced Nova. When in close proximity, the Elcor husk will jump a few feet into the air and send out a shockwave in all directions. Be wary as this does decent damage.(Similar to Nova, but a lot more deadly)
Volus Husk Shields
Powers and abilities.:Maintenance Drone:When released, it replenishes the shields of the volus husk.When in cover, the volus husk will roll up into a ball and head in your direction in order to close the distance. It will then proceed to toss proximity mines in groups of 3.
Salarian Husk Shields
Powers and Abilities:The Salarin Husk has the ability to deploy reaper barrier generators in order to boost the effectiveness of other enemies in battle. It also has the ability to create 2 decoys in order to trick the player into thinking it is located somewhere else.
Drell Husk (Slasher)
Powers:Biotic Charge and Omni Blade. The Drell Husk will attempt to get up close and personal by using Biotic Charge. If you stay too close too long, The drell husk will one hit kill you with a miniature version of the omni blade.
Quarian Husk (Overlord)
Powers:Tech Armor.Assault of the Elements: While the Quarian husk snipes from a distance, it is able to dispatch a very powerful attack(courtesy of reaper improvements) that is a hybrid of Incinerate, Cryo Blast, and Overload.
Powers: Cluster grenade.
Powers:Can move quickly in all directions(similar to asari multiplayer movement) Like the Saren husk in the original mass effect, the adjutant will fire several biotic warp attacks in succession from its right hand to keep you on the move. If you try to attack it head on with standard weapons, it will use its right hand to emit a barrier to deflect bullets. Only way to take it out is to use heavy weapons, attack while it's attacking and hope for the best, or flank it.
Harvester Self Explanatory
For the final faction, assuming we get to see more of them, Collectors
Harbinger(starts after about wave 7 in bronze, 5 in silver, 3 in gold)