
It's always best to use the ammo power that deals bonus damage to the first protection layer that will be damaged by a shot, even if that protection layer is only at minimal strength and most of the damage from a shot will also be applied to the layer underneath.
Using the right ammo power is essential for one-shotting enemies with protection. However, once said protection is gone, a clean headshot still inflicts impressive and often fatal damage. At higher difficulty levels where most enemies have protection (shields, barriers, or armor) the Mantis loses effectiveness as a "one shot, one kill" weapon. However the M-29 Incisor in turn may be superior to the Mantis for squadmates see its page for more information. The Mantis is superior to the M-97 Viper for NPC squadmates since they do not take advantage of the Viper's rapid-fire ability but only use single aimed shots just as they do with the Mantis, which will result in much less damage. Other classes that choose sniper rifle training on the Collector Ship don't have these tools to call on and may find it more effective to use either the semi-automatic M-97 Viper or burst-fire M-29 Incisor which have more forgiving ammo capacities and firing rates than the Mantis. Infiltrators and Soldiers have the easiest time lining up precise and highly damaging headshots using Adrenaline Rush, Tactical Cloak and the time dilation effect of the Infiltrator's class skill. This power is offset by a low rate of fire and a low ammunition reserve. The Mantis is a powerful and precise single-shot sniper rifle, able to kill most lower-ranked enemies with a single headshot, often even at higher difficulties with the right damage modifiers.
Squadmates deal 45% less damage with this weapon than if wielded by Shepard. This weapon can be used by Garrus, Legion, Thane, and Zaeed. You get this weapon automatically when you start the Freedom's Progress mission as a Soldier or Infiltrator. The prevalence of kinetic barriers has made this weapon less popular with the military, but it is used more frequently in the Terminus system where these defenses are less common. Manufactured by Devlon Industries, the Mantis is primarily used by police and planetary militia groups. Effective against armor, but weaker against shields and biotic barriers. Incredibly accurate at long range, but rate of fire is slow. Powerful sniper rifle able to take out most targets in a single shot.