The Mantis is a powerful sniper rifle which is able to take out most targets in a single shot. It's incredibly accurate at long range, but rate of fire is slow. Manufactured by Devlon Industries, the Mantis is primarily used by police and planetary militia groups.
In multiplayer, equipping a high level Mantis with the Piercing Mod along with the Infiltrator's pairing of Tactical Cloak and class specific passive powers (with damage focus), it can yield a massive punch to difficult enemies.
A Piercing mod can turn the Mantis into a weaker, but much lighter version of the two Widow rifles and the Javelin rifle. While it can take time to get the mod fully upgraded, it can, with the right upgrades or mods, make this rifle a sufficient replacement for the Widow rifles and Javelin rifle.
The Mantis is a very powerful weapon from the get-go. Its weight can be reduced to make it a fairly useful rifle even for power-intensive classes. With the ability to one shot kill basic troopers with a headshot, or cripple shielding of tougher enemies, the Mantis is more than capable of dealing with enemies on the hardest difficulties without sacrificing too much recharge speed. This becomes even more apparent in the hands of a Batarian Sentinel, where its net can hold enemies in place, and upgrades to capacity can greatly improve power recharge, and then the damage it inflicts can be fatal to most enemies.
The Mantis X, with an Extended Barrel V in the hands of a character invested in weapon damage increasing powers is capable of one-shot headshots on all unprotected infantry-level enemies.
Used in tandem with Overload, one can use the power to destroy a Centurion's, Nemesis's, or Marauder's shielding then proceed to headshot them and kill them instantly, even on Gold difficulty.