Mimic Beacons can be tossed into an open area, without any cover, to provoke the enemy into targeting the temporary holographic target instead of one of your other soldiers. In most cases the enemy will then waste a turn killing the hologram.
If the hologram is destroyed before the enemy turn ends, any hostile units that have not attacked will still be free to target your soldiers.
Thrown exactly like a grenade, but can't be shot from a grenade launcher.
The hologram seems to match the soldier who throws it in appearance.
The hologram can not take cover.
The hologram has fixed 12 HP.
Throwing a Mimic Beacon will break concealment.
The Mimic Beacon decoy is immune to all status effects and cannot be moved via Tongue Pull or Binded.
Mimic Beacons will fool almost all aliens and ADVENT forces, including robotic ones, into attacking it, regardless of if other targets have higher hit chances. Only Faceless themselves are not fooled and will completely ignore the beacon.
Mimic Beacons are an incredibly powerful tool when used correctly. The ability to "panic button" a beacon when something goes wrong can allow for riskier moves (a skullmining or evac) as well as providing a means to escape a situation that has gone awry.
A Mimic Beacon thrown outside of cover will generally see the enemy focus it down. Especially in later parts of the game, its generally somewhat difficult for a single pod to kill more than one full-HP soldier: the beacon itself.
Beacons are expensive, but supply is primarily limited by Faceless Corpses, which are somewhat rare. It is therefore highly recommended that you do the following;
Never Sell Faceless Corpses on the Black Market
Win Retaliation Missions
Allow the Faceless Dark Event to complete
Faceless are generally the weakest enemy in XCOM, and are unlikely to really throw a game away like some of the other events.
It is helpful to take two Mimic Beacons on a mission;
Mimic Beacons, once you realize their power, will be incorporated into your tactical decision making. In the event that your carrier goes down, this might seriously undermine your plans and overall resilience of the squad. Having a back up ensures that losing one does not seriously degrade your tactical situation.
On most missions, where there are roughly 4+ pods, Mimic Beacons can help deal with most of them. 1 pod is killed from concealment, 2 pods are taken out with the help of Mimic Beacons (if necessary), leaving only one pod where you could conceivably have to take most of the missions' wounds.
The usefulness of Mimic Beacons tends to fall off later in the game when there are more powerful alien units that can take out a beacon with fewer actions, and other damage-dealing or protective options like utility armor items or grenades are able to assist more with the mission.
A Combat Hacker build Specialist is one of the best candidates for carrying the Mimic Beacon, as they are generally not front-line troops and therefore benefit less from most utility items in their arsenal, with the exception of the Skulljack with Skullmining. Having them carry the Mimic Beacon frees up a slot from other squadmates who would have to carry it and allows them to support the team more when things go wrong.