Originally issued to the salarianSTG to allow small units to contain much larger enemy forces, the Scorpion pistol now sees service galaxy-wide. It fires low-velocity, squash-head projectiles with a dual use. The high-explosive filler within the projectiles contains an adhesive that secures the projectile to the target on impact. When fired into a surface, it turns into a proximity mine.
If Shepard has the Scorpion equipped in the pistol slot during the final sequence of the Mars Archives mission (possible only if imported from a previous playthrough), it will always fail to stop Dr. Eva's final attack: the initial strike does too little damage, and she will reach Shepard, initiating the cutscene where she kills Shepard, before the rounds detonate. Having the Scorpion equipped at that point guarantees death; restart from an earlier save where the weapon can be de-equipped.
The Scorpion is unique in that it fires explosive projectiles similar to sticky grenades instead of conventional slugs. Shots detonate roughly three seconds after attaching, therefore damage is not instantaneous.
If the slug is fired to the ground and not attached to an enemy it acts as a proximity mine and will detonate immediately if an enemy is nearby. Players can take advantage of this characteristic of the gun to work around the detonation delay of the slug in the heat of battle.
The biggest problem with the Scorpion is its very low clip and reserve capacity. Accuracy is critical to using the Scorpion effectively, though this is somewhat mitigated by the explosive nature of the shots.
In addition, the Scorpion is very heavy for a pistol, meaning that classes reliant on powers may be forced to use another weapon. (This can be mitigated with the Ultralight Materials mod that comes with the Mass Effect 3: LeviathanDLC.) However, squadmates' power recharge times are unaffected by weapon weight.
The Scorpion's biggest strength is the explosive manner of its rounds, which can result in taking out multiple enemies with a single, well-placed shot. It can give a small level of lenience if a shot is misplaced, as the explosion can still do considerable damage.
The shots from this weapon can effectively turn the Scorpion into a "mine launcher". This allows deadly ambushes to be created and can ease some of the pressures of an overwhelming force.
The Scorpion's slugs can also be used as "cover-denial" when facing enemies using a corner as protection: launch a quick salvo at the corner the enemy is taking refuge; the resulting detonations will severely maul, if not kill, an enemy.
Most human enemies will panic when a round sticks to their body, interrupting their actions and drawing them out of cover. This can be useful on higher difficulties, even when a single round may not kill them outright.
It's worth noting that the effect of ammo powers activate when the shot hits the enemy, and the effects remain until detonation. Because the Scorpion has a high chance to activate the effect on hit, this can make a Scorpion enhanced with Cryo Ammo deadly to unarmored enemies. On Normal difficulty, it is possible to one-shot unarmored Cerberus troops with this combination.
Due to the "sticky bomb" nature of its munitions, mods that increase penetrations are useless here.