Security cameras:

All the main games except the forth and the sixth have a security-camera sytem,which observes the animatronic characters. One location can be viewed at a time,and some 

areas are not visible on the cameras. Most camera feeds 

are dull,sometimes almost black and white in color,and full of 

video noise. In the third game,the cameras stop working 

if their associated system fails. Cameras are used in the fifth game as a mechanic in the fake ending and custom night.

Lights:

Lights in the first and second games are activated with buttons on the walls and illuminate the player's blind spots: the doorway or vent exit,respectively. The lights are similar in the fifth game,but are mounted on a control pad and illuminate the animatronics rooms. The flashlight in the second game had a finite battery life,the flashlight is also used in the sixth game,but it is automatically turned on when the player looks at the vents,and has unlimited power.

Doors and Vents:

Doors and vents are a common feature in all of the games. 

The firts and fourth game have doors to be closed when an animatronic is near. Doors are also present in the fake ending and custom night of the fifth game with the second,third,and sixth games,as a medium through which animatronics can get to the player. They are also present in fifth game as the primary means of transport for the player.

Jump scares:

Jump scares are in all of the series main games when any animatronic reach (and attack) the player. In most jump scares,an animatronic character suddenly appears in the player's view followed by a loud bellow. Some jump scares,including those bye Golden Freddy (in the first game),Nightmare,and Nightmarionne,consist of a single screen with can use tools to prevent attacks (and jump scares)

Minigames:

In all games except the first,the player gains access to a series of (predominantly eight-bit) minigames-randomly after death,of after completing a specific task. The minigames usually relate to a story or event relevant to the game. 

Phone calls:

In all main games except the fourth,fifth and sixth the player receives a telephone voice message from a previous worker (or owner) of the player,describing several gameplay mechanics and outlining the location's backstory.

In the firts and second games,the voice in the messages is the same,but in the third game,it have a California accent. Phone calls from the first game can be heard in Five Nights At Freddy's as an Easter egg. 

Easter eggs:

Almost every game in the series contains some Easter eggs and rare screens,some of which point to the lore. They are often presented as hallucinations,with some examples including the "It's Me" phrase in the firts game,Shadow Freddy in the second,rare William Afton's corpse screens in the third,various random items appearing near the bed in the fourth,rare blueprints in the fifth,and rare back alley screens of animatronics in the sixth.