Flashlight is a vital mechanic in Five Nights at Candy's 3.
It lets the player see around the Bedroom, and enables them to scare off Monster Rat, Monster Cat, Monster Vinnie and Shadow Rat by flashing the light into their eyes.
Normally the Bedroom is surrounded by darkness. There is a small circle around player's mouse that partially brightens the room, this is the flashlight. The flashlight is a vital mechanic, as it makes you able to spot any threats around the room.
Another purpose of the flashlight is to scare away Monster Rat, Monster Cat, Monster Vinnie and/or Shadow Rat. Once the player hovers over Monster Rat's, Monster Vinnie's, or Shadow Rat's eyes, thus flashing the light on them when they are at the bedroom's door, wardrobe or closet, it will repel them for a short time period.
Once they are in the room, player must do the same to avoid getting killed. However, Monster Rat, Monster Vinnie, and Shadow Rat will try to dodge the flashlight in this situation. The flashlight, when used in combat, acts against a timer, based on shining the light in the monster's eyes continuously, as well as flashing the monster's eyes for a certain amount of time total before the combat time ends.
Finally, it is also used to make them leave the room. After the previous situation mentioned above, Monster Rat, Monster Vinnie, and/or Shadow Rat will always go underneath the bed, best indicated by the sound cue. The player must then look under it, and figure out under which side of the bed they are hiding.
Then turn the flashlight away from them, and while above the bed in the room, flash the light on the opposite side of the room. It will make so the monster will peek out their head on the other side, which is when the player must flash the light onto their eyes. Performing this operation correctly will make them leave the room.
The flashlight is used to keep Monster Cat at bay similarly to the other characters, but for Monster Cat, all you need to do is flash the light onto either side of the bed when they appear in order to scare them off for a short time period. You do not enter combat when shining your light in Monster Cat's eyes.