The Left Air Vent is a location in Five Nights at Freddy's 2. Balloon Boy, Toy Chica and Bonnie will go in these vents to get to the office. On very rare occasions, the Endoskeleton can be found in the vents. Once an animatronic passes through the vent, they will appear in the Left Vent blind spot in the office, where the player will have to put on a Freddy Mask to avoid them entering; however, Bonnie does not do this. The light however if shown will stun Bonnie in the vent and may take them a little while to attack.
Just like the Right Air Vent, the Left Air Vent looks just like a regular air vent and to see the animatronics you must use the light that has been equipped inside of the vent.
Animatronics who go here
Toy Chica can be seen in a sort of crouching position as she is on her knees in the vent and she still does not have her eyes or beak. Withered Bonnie Will appear with no arms sticking out: he only sticks his face into the vent camera. Balloon Boy will appear with one arm sticking out, as if he was army crawling through the vent to get to you.
It is very easy to counter animatronics crawling through the vent. Just shine the light to see the animatronic.