Scion

Scions are a type of Husk made from three human Husks fused together and grafted around a single mass effect/biotic weapon on the left arm. The blue "sacks" on their backs contain redundant organs and element zero sources to provide power for their weapons and shockwaves.

Mass Effect 2
Scions operate alone or in pairs, hanging back as Husks and Abominations rush ahead. Less mobile than other Husk variants, Scions provide ranged fire support, lumbering behind the wave of attackers while firing weapons and discharging biotic attacks.

Capabilities
Offensive

Scions are armed with a powerful shoulder-mounted cannon, which fires an advanced version of Shockwave that will travel longer distances, penetrate thin cover, deal heavy damage, increase the recharge time on your shields (although this can be countered with Tech Armor, Geth Shield Boost or Unity, as well as an Emergency Shielding research.) and mildly knock back you or your squadmates, all even on lower difficulties. At close range they will be able to create a different blast wave that will deal more damage to your shields the closer you are.

Defensive

The Scion is heavily armored, but does not possess any barriers, shields or health.

Tactics
General Notes
 * Unlike other enemies, there are several weak spots on a Scion's body that you can exploit:
 * Firstly, their head is located on their right 'shoulder' and shots landed there will deal greatly increased damage.
 * The hump on their back also receives more damage.
 * Finally, there is a bright blue circle on their backs, but it is only safe to target when the Scion is distracted by your squadmates or a Combat Drone.
 * In terms of weapons, any player class that has a sniper rifle will have the advantage in a fight against a Scion. This allows you to keep the fight at a distance and have room to dodge its attacks. Paired with Armor Piercing Ammo or Incendiary Ammo, this would be the best combo against it. If the sniper rifle is not available, the Collector Particle Beam is an efficient alternative.
 * In some encounters, the Scions remain stationary and inactive if you keep your distance (the distance that doesn't trigger the HUD to display its health). You will then be able to shoot it from afar without it ever moving in to target you.
 * If Shepard chooses Stasis as his/her bonus talent, he/she can use it to disable the Scion and take out the supporting husks easily, without having to worry about the Scion's devastating attacks. If the Scion is on the edge of an area, Shepard can also use Stasis on the Scion, and when it comes out it may fall off the ledge and die.
 * Flashbang Grenade is a useful means of disabling the Scion's main attack.

Class Specific Notes
 * An Adept's Singularity can keep a Scion rooted in place and unable to attack for a short time.
 * Vanguards can use Charge to quickly close with a Scion, bypassing its deadly long range attack. Once in close combat, players can backpedal away from the Scion, ideally moving far enough to avoid its close combat burst attack.  This strategy can be repeated again and again, triggering the Scion's close combat attack only to move out of range before it fires.
 * Engineers can use Combat Drone to keep the Scion locked into a stunned state; high-level or evolved combat drones attack and stun the Scion faster than it can ready an attack and will also distract it. In the meantime, you can attack the Scion with Incinerate and weapons. The Combat Drone will only be nullified if its time runs out, if it is attacked by another enemy, or if the Scion uses its shield disrupting ability, but the Combat Drones can be almost immediately re-cast.
 * Soldiers armed with a strong sniper rifle or longrange, devastating weaponry like Carnifex or Vindicator can utilise their Adrenaline Rush to the extreme in fights against Scions. If used at the right moment, the Soldiers can get a clean headshot at to the head on the right side of the Scion, depleting its Armor at a very fast rate, while keeping a nice distance.

Mass Effect 3
Scions return in Mass Effect 3's multiplayer with the Retaliation Pack DLC.

Capabilities
Offensive

Scions are armed with a powerful arm-mounted cannon that fires explosive shots with great radius in salvoes of three. Up close, they can instantly crush the players should they get too close. Like any other Collector unit, they can also be possessed, becoming far more powerful than usual.

Defensive

Scions possess powerful armour that compensates for them lacking health, barriers or shields. Like any armoured enemy, they cannot be grabbed for an insta-kill.

Tactics

 * Similarly to the Ravager and the Geth Prime, the Scion fires its arm cannon in salvos of three. Time your return fire to make use of the pause.
 * While the Ravager, Atlas, and Geth Prime can fire right away, the Scion actually needs a few seconds to hold up its heavy arm cannon to fire, which gives you enough time to get behind cover. They can't move to shoot with their cannon up, having to put it down before moving to a new location. This is helpful for hit-and-run game play.
 * The rounds from Scion cannon have a huge explosive radius, allowing them to deal great damage to whole groups of players.
 * Destroying the sacs located on their back decreases the damage that their cannon attack deals. Deploying Combat Drone can be very helpful in getting them to turn around. Destroying these sacs also causes significant reduction of their armor.
 * If a player uses some kind of scanning ability such as Recon Mine, Hunter Mode or Tactical Scan the Scion will be highlighted, but the sacs will not be. Use this to make it easier to hit the sacs.
 * Powerful sniper rifles with sufficient piercing such as the Javelin can hit both the head on the front and the sacs on the back in one shot, resulting in massive damage.

Trivia

 * In horticulture, the term 'scion' refers to a method of grafting plant tissues together.