Don’t let oxygen hit zero. Don’t breathe when the hunter is watching. Don’t ever peek around the corner no matter what you hear or don’t hear. It has three stages: Stalking. If it hears something, like a breath, then it goes into hunting. Hunting. Do. Not. Breath. Oxygen consumption is doubled. Elsewhere. Safe to breathe, until it returns.
Credits to @tacocat6564 for the game idea I slowed a bunch of animal sounds down for the noises Slight g0r3 warning, your head gets eaten, but you can toggle gore.