Atlas

The Atlas is a large Cerberus mech encountered in Mass Effect 3. While they tower over any human, they have a weak point in the cockpit where the driver sits. If the driver is killed before the Atlas mech is destroyed, Commander Shepard can gain control of it and use it as a vehicle.

Capabilities
Offensive

The Atlas is equipped with a powerful rocket launcher and a rapid-firing mass accelerator cannon. At close-range, it can pick up enemies with its claw and instantly incapacitate them.

Defensive

The Atlas possesses extremely durable shields and armor, and can shoot smoke grenades.

Tactics
General Tactics
 * The Atlas is slow and makes for a large target, but should not be underestimated. When attacking the Atlas from the front, take cover immediately and watch for when it moves its rocket launcher arm to fire. Under no circumstances should an Atlas be attacked at melee range; the Atlas can easily grab the player for an instant kill. Sustained weapons fire and powers should eventually destroy an Atlas provided the player can attack from a safe distance and in cover.
 * The Atlas' cockpit window can be shattered after its shields have been taken down. This requires a considerable amount of sustained fire, but breaking the window will leave the pilot vulnerable to attack. Killing the pilot will destroy the Atlas immediately in Multiplayer. In some instances in single-player, however, this will leave the Atlas intact and able to be piloted by the player.
 * An even faster way to destroy the Atlas is to shoot at the eezo drive. This is however at the rear of the Mech, so get your squadmates to keep it busy while you go around it.
 * The Atlas can be successfully attacked with Sabotage and turned against other nearby enemies.
 * In Multiplayer, a single Cobra Missile will instantly kill an Atlas and if well placed, can take out multiple Atlas mechs at once. Note that this is only possible on Bronze and Silver level challenges. Gold level Atlas mechs need half of their shields to be removed first for the missile to kill them in one hit.
 * The Weaken Armor evolution for Warp can quickly deplete the armour of an Atlas.
 * Any class capable of throwing any type of grenade that will explode on impact, can do considerable damage to an Atlas. This technique works especially well if staying close to ammunition boxes, as you can get new grenades when you have used your own.
 * If upgraded, Pull can stagger an Atlas for a few seconds.

Class/Character-Specific Tactics
 * In Multiplayer a leveled Nova can cause considerable damage, and bring this behemoth down fast. However, this is risky as it can leave you exposed to a counterattack from the Atlas, or any ground infantry with a clear shot.
 * An Infiltrator can throw Sticky Grenades at an Atlas while cloaked at relatively low risk. If the Atlas is not currently attacking any enemy, it will turn towards the location the grenade was thrown from and shoot with its accelerator cannon. To avoid this shot, don't remain stationary while (or after) throwing grenades.
 * An Infiltrator can use their Tactical Cloak, with the M-98 Widow, and the right upgrades, can take down an Atlas in just a few shots.
 * In Multiplayer, turian Sentinels are very effective against Atlas as they have the ability to deal damage to their armor and shields. They can strip the shields with Overload and then take down its armor with warp. When combined with decent weapons, a turian Sentinel can dispatch an Atlas quickly.
 * A krogan's heavy melee can cause an Atlas to stagger, making them the only characters where melee is a viable tactic. Caution should be taken of course, as the Atlas will not always stagger and is likely to retaliate with its own, more powerful melee.
 * Like the Sentinel, the Engineer has several powers effective against the Atlas. These include Overload and Incinerate as well as Combat Drone. The latter is an excellent distraction, and the former two are effective against the Atlas' shields and armor, respectively.
 * In single player, a soldier with a high leveled Adrenaline Rush can cause a massive amount of damage in a short period of time.

Trivia

 * According to The Art of Mass Effect 3, the Atlas were first intended to be a heavy version of the YMIR Mech with a soldier inside. Eventually, a canopy was added to protect the soldier, and the Atlas gain a larger size than the YMIR Mech.