ADVENT MECs are armored targets, thus reducing all received damages, but are vulnerable to shredding.
MECs are first deployed in mid-April (late April on Legend) as squad leaders for ADVENT pods, followed by Troopers, Stun Lancers and later by Shieldbearers. Later in the game (late June or mid-August on Legend) the Heavy MECs take their place while the normal MECs become support troops for ADVENT pods (but not for Aliens). In the very late game, normal MECs are totally phased out and Heavy MECs take their place as support troops.
Heavy MECs have more HP (12/14/15/18), +1 Armor, +10 Defense, better hacking defense (80/80/90/90 Tech) and much better damage (8-9 shred 2 with main gun, 3-5 shred 1 with micro-missiles). They have +5 Aim on Rookie (which makes their aim the same on all difficulties) and 15 Mobility on Veteran and above.
ADVENT MECs are large autonomous robotic units that provide heavy support for other ADVENT units. They are similar to the XCOM MECs of Enemy Within, but are completely robotic in their exterior, and are a glistening white (basic models only). They carry a variant of the Magnetic Rifle that is monstrously large in both size and damage output. Additionally, ADVENT MECs have an automatic grenade launcher on their back, allowing them to fire a fusillade of micro-missiles in an AoE attack. ADVENT MECs are heavily armored, and have superior health to ADVENT troopers, as well as damage reduction in the form of armor points. As robotic units, they are vulnerable to hacking and having control of them given to XCOM for a short while, although a failed hack will increase the MEC's accuracy and defense. A successfully hacked MEC that has been turned against its ADVENT masters is a potent tool in the hands of an XCOM commander; its combination of high health, tough armor, powerful weaponry and a missile barrage can have a dramatic effect on the course of a mission. Also; being robotic units MECs are vulnerable to EMP weaponry such as EMP Grenades and Bluescreen Rounds. A Psi Operative can also make use of the Fuse ability to detonate its grenades remotely, despite being a robotic unit.
- It is possible for a Specialist to hack ADVENT MECs. But if the hack fails, either the MEC's Aim and Dodge stats will be increased, or there is a chance of summoning reinforcements.
- Micro Missiles have 20 range and 1 use on normal MECs and 2 uses on heavy MECs.
- MECs, like other enemies with AOE abilities, will strongly favor their Micro Missiles ability if they can damage more than one unit with it. If you end your turn with two or more soldiers grouped behind the same cover near a MEC, Micro Missiles can destroy your cover: consider hacking, disabling or simply killing a MEC before it gets a chance to expose your squad to enemy fire.
- The advanced version of the ADVENT MEC tends to immediately enter Overwatch when revealed, instead of moving when found.
- While MECs have been observed "jumping" to higher elevations, they do not appear to have the "Leap" ability, like the Faceless. This jump animation is used to signify a MEC ascending a ladder, drainpipe or scalable feature.
- There is a glitch that sometimes occurs if the player uses the haywire protocol on an Advent MEC, and saves and reloads right before the hack begins. This will result in the player's GREMLIN following the MEC instead of the specialist.