The Fallen is based off a creature from the multiplayer horror game Damned and from the Weeping Angels seen in Doctor Who.
It is an angel statue covering its face. Folklore states it cannot move if you keep eye contact with it, but The Fallen can still move when watched. In game, it moves like a chess piece. Its hands move slightly when attacking.
She is able to place down a decoy of herself, which can be useful in many situations. But if a player or group of players run into the decoy and touch it, they will trigger an alarm and the person playing Fallen will be able to see an outline of the affected players through the wall. She can also teleport back to the decoy at any time, leading to a dangerous combo.
Fallen's ability allows it to create a decoy fallen that acts as a trap for unsuspecting survivors. When you place the decoy, it plays the sound of Fallen's taunt, and survivors could mistake it for you. If a survivor gets near or touches the decoy, you can activate your ability again to teleport back to the decoy, but you can only have one decoy at a time. Knowing this, you want to be careful, and use it sparingly.
Fallen can have a hard time in the beginning, as fallen is quite slow. However, if you do manage to take down a survivor, place a decoy on their dead body. This will ensure their death, and will also tell you if they have second wind, so you can catch them trying to escape. However, they will know if you place a decoy, as it will sound a taunt. Try taunting very rarely to make them think you placed a decoy.
If fallen catches you off guard, you can have a hell of a hard time getting away, especially if it places a decoy on your dead body. If second wind activates, hope to god that you get up not touching the decoy, or hope that Fallen is too distracted to teleport away. If you hear a taunt coming from Fallen, always assume that it placed a decoy, unless you hear it moving. If you see fallen, stand still for one second to make sure its not a decoy.