This is Guiding Light.  Whenever you die, Guiding Light will speak to you. He'll give you tips to avoid dying next time and will inform you of the monster that killed you. If you are lost in a room and can't find a key, he will light the spot where the key is, in a bright blue light.  When a player is being chased by Seek, Guiding Light will highlight the doors you have to take to escape. When a player is trying to find the key code for Door 51, Guiding Light will highlight the books you need to take. Guiding Light also lights up the switches in the Electrical Room for you to collect as well as lights up the lever in Door 61. According to the Doors Wiki, Guiding Light will prevent Seek from chasing you any further, locks the door shut, and will break a lamp to distract the Figure for you. This is a friendly entity, and it'll help you on your journey to Door 100. 

This is the Figure.  It is one of the main bosses on Floor 1 and the most dangerous. It appears on both Doors 50 and Doors 100 so expect these rooms to be insanely difficult. It is unkillable and can only be momentarily stunned by the crucifix (Items & Collectibles). The only actions you can do are to hide and run. If you hide in a closet just before the Figure gets you, you'll be safe. The Figure has a weakness which is that it is blind, however, its hearing is impeccable. Whenever you are around the Figure it is best to crouch so it doesn't hear your footsteps. It is faster than you unless you use vitamins (Items & Collectibles). The Figure's footsteps are loud so you can tell when he is coming near you. At Door 50 and 100, he always uses a particular route however he will deviate from it if he hears you. The Figure will instantly kill you in one hit. The Figure is relatively easy to deal with. Just DON'T be heard.

This is Rush.  It is the most common monster and chances are it will be the one to kill you. There are multiple indicators that it is about to show up. First the flickering of lights. If you miss this indicator, there is a slight noise that can be heard like a car zooming towards you just before he gets you. The only way to survive Rush is by hiding in a closet, cabinet, or under a bed. If you are in one of the basement levels where you have to flick the lever to open the gates Rush cannot kill you. Rush cannot kill you if you are in the skeleton key room. Rush also cannot kill you on Door 100 because it cannot intervene when the Figure is present. According to DualShockers, "Once this ghastly foe hits an unopened door, it will disappear, and players can safely leave their hiding spot." Thus, when you see the lights, flicker do NOT open the next door unless closets are not within your vicinity. This action ends Rush early, and you can move forward without wasting time. If you decide you've had enough of Rush and want to get rid of him, there is a way. That is through the crucifix although it only kills him one time and worse, Rush can come back.  If you are caught by Rush, you will instantly be killed. The general tip for this monster is to hide and FAST. 

This is Screech. Screech is probably if not the most annoying monster in the game. The biggest indicator that Screech is attached to you, is the sound it makes. It's a little "Psst" sound. Screech only appears when the room is dark and all light in the room is gone. Light from your flashlight, lighter or candle will get rid of it, however. Screech is attached to you, so to get rid of it, you just have to start looking around, moving your console until you look at him. Once you look at the Screech, it will go away. It can appear multiple times, and if not seen by you, it will take a portion of your health. You can kill it using the crucifix however it is not recommended to use such a weapon against a minor entity. 

This is Snare.  Snare has the same annoyance value as Screech. Snare only appears from Doors 90 until Door 100. Snare is only deadly because doors 90 through 100 are dark unless you have a flashlight, lighter, or candle. Without a light source, you have more of a chance of falling into Snare because it's nigh impossible to see. Snare will take a portion of the player's health if walked on and will stun the player momentarily too. This is deadly especially in Doors 90 through 100 because Rush appears way more often and can barely be heard at that stage. It is best not to underestimate Snare however it is rather harmless. 

This is Jeff. Jeff is always in Door 51. He sells the player multiple useful items. You can buy multiple items from his shop, and you can also tip him for his service. If you fill his tip jar Jeff will be happy and do a little dance. He is a rather docile and friendly entity.  When Rush comes, Jeff will close the shop and hide. If you switch the music on his radio, he will be angry and switch the music back. This is the same if you shine a light on him. Jeff can sell you a range of multiple items and they are ALWAYS useful. He can sell you a crucifix, flashlight, lighter, vitamins, skeleton key, and lockpicks. 

This is Void. Void only appears if the player is lagging behind a group. If you are too far from your group Void will damage you, but will not kill you unless you have low health and will teleport you back to where you are supposed to be. Void can also teleport you if you are playing by yourself, in case the room doesn't load properly. According to the Doors Wiki, it can be killed by the crucifix and deal no damage to you, however, you will still be teleported back to where you are supposed to be.  Void has no physical appearance. 

This is Dread. Dread only appears if the clock has struck midnight. It is easy to check the time when looking at a wall clock or a grandfather clock in a room. Dread will slowly follow the player until the next door has been opened. Dread can be crucified and according to the Doors Wiki, it will be killed for all other players running with you. During Dread's chase, your hearing will be stunted making Rush and Ambush more dangerous. As Dread gets closer to you, it gets more louder. Dread will instantly kill you once it reaches you.