Player has to deal with asphyxiation or limited supply of whatever substance they require for breathing (such as oxygen). Including situations that remove or supplant the breathable substance, such as drowning, vacuum, gases, etc.
Alternate names: Oxygen, Drowning
See also: airflows
(may cause asphyxiation by depleting breathable air from an area), ventilation
This covers things like drowning (liquid filling the respiratory tract preventing breathing), asphyxiant gases or other depletion of breathable air or such in the area, vacuums, and other methods. Strangling is not included unless the game specifically simulates asphyxiation for it rather than just causing damage/death.