Air Bender is an achievement awarded for obtaining 30 human kills in Metro 2033, and 50 in Metro 2033 Redux, both using pneumatic weapons only, either with the Tihar or the Helsing. Obtaining the kills does not have to be consecutive nor with the same weapon. Any kills will be added up over one playthrough. Front Line is an excellent level to accumulate kills, as both of these weapons can be found in the level for free. It can also be earned at the same time as the Air Gunner achievement as that requires 30 enemies, human or non-human, to be killed with pneumatic weapons.