The Entity's weakness revealed and proved.
Have a seat and have fun reading because we're going deep boyos.
Part 1 - The Different Realms 
The first part of uncovering the Entity's weakness is to understand the world the Entity has created. We know that the Entity's realm is a realm of it's own. A nighmarish construct where the trials happens. The MAIN realm where everything happens. But there are also two sub-worlds that exists within that realm.
The Dream world
This realm can only be accessed by being put asleep by Freddy's power and by Freddy himself. I will not add any more information about it, since this realm is not the important one for us to prove the Entity's weakness, but by existing, it proves that multiple realms can exists within the main one at the same time.
The Spirit world
This realm can be accesed willingly by the Wraith himself due to the power of the Wailing Bell and can also be accessed by the Nurse herself due to the power of Spencer's Last Breath. This realm is THE most important one for us to prove the Entity's weakness. So we will focus on this one.
Part 2 - Particularities of the Spirit World
The spirit world is characterized by many things, we will go through the important ones. So let's start.
Particularity 1 - When entering and leaving the realm, a certain effect can be seen.
The effect is also present when a survivor gets sacrificed.
And can also be observed when the Entity appears on a hook.
This single effect proves one thing ; Amongst the Wraith and the Nurse, the Entity and the survivors have access to the Spirit World.
The nurse doe not have any effect like this, since she pierces throught the Spirit World, ergo there is not enough time for the effect to even appear. Also as you can see, the survivors enters the spirit world when being sacrificed to the Entity. The Entity itself is also capable of entering and exiting the realm at will. You can clearly see it when the Entity does the following ; Blood Warden effect/Window Block/Sacrifice sequence. This is the important point of this particularity.
The Entity can enter and leave the Spirit world at will.
Particularity 2- Beings inside it cannot be seen.
This one is quite self-explanatory.
Particularity 3- Anything affected by the Spirit world is weak to any intense light.
First let's have a look at what is affected by the Spirit World in-game. It is quite simple, anything that has an effect similar to the 1rst particularity is affected. This means the following killer powers ;
- The Wraith gets a stun AND a blind effect if you manage to blind him while he is inside the Spirit World. Why ? He is inside the Spirit world.
-The Nurse goes instantly into fatigue mode if you manage to blind her while she is charging her blink. Why ? Her charging her blink is a preparation to pierce throught the Spirit World, and you can clearly see small orange sparks and lights in her left hand while she charges. This is the effect effect of the Spirit world.
-The Hag's traps disapears when you flashlight them directly. Why ? When you finish placing a trap, you can clearly see the outline of the circle of activation. This circle has the SAME effect of small orange lights of the Nurse's charging blink and the Entity's blockers at windows. Which means it is affected by the Spirit World.
And guess what, theses killer powers are the ONLY ONES that the Entity gave a part of it's own power, and they are the ones heavily weakened by the flashlights while other killers are not.
Oh, another fun fact ; The legacy items like theses ones : 
Have the following description to them ; The touch of The Entity leaves burning scars and blisters of light. Is it a gift or a curse? And as you can see, it is the same orange color which is characterized by the Spirit World.
All that said, where does that leaves the Entity and it's weakness ? Well, we proved one thing at least.
The Entity has its home in the Spirit World.
But since it has its home there, how do we bring light to it?? Well...
Part 3 - The Red Stain 
The red stain is a mysterious light coming from the killer's eyes, and might be the sole reason of why killers are extremely weak to flashlight. Indeed it comes from the killer's eyes, but it does not originates from the Killer. It originates from the Entity itself. The Entity needs to see throughs his puppet's eyes in order to truly judge how well he/she did, or just for amusement. The claim that the red stain comes from the Entity can be linked to a single perk.
Beast of prey is a perk from the Huntress, and it states the following ;
Your lust for a kill is so intense that your connection with the Entity is momentarily lost, making you totally unpredictable. The Red Stain disappears when Bloodlust activates.
This ties directly the Red stain to the Entity and to the Killers. Which is also backed up by the Devs answering the following question ;
WILL THE ENTITY EVER TAKE KILLER FORM?
"The Lore reference says that The Entity is taking the Killer form all the time."
And knowing that, where does the Entity resides again ?
Oh that's right, in the Spirit World. The same world that is vulnerable to intense lights. Which is the same world the Entity's stays while seeing everything through the Killer's eyes and also why the killer is so weak to flashlight to the point of stoping everything they do in order to protect themselves from the light. Since if you blind the Killer, you also blind the Entity.
A point has been proved here ;
The Entity is weak to flashlight.
Part 4 - The Generators. 
These are the most common yet most controversial things in the whole trial. The Entity is weak to light, yet generators generate light. And if all generators are activated, they all light up and power the exit gates. Now, why would the Entity bring light if it is it's major weakness? Well, for the same reason flashlights exists ; Both of thoses things are not entirely made by the Entity.
This phrase has been said to the Killer during the tutorial when breaking a generator ; Do not let the light in!
This proves that the Generators were not only powering the exit gates, but they were also created as a means to weaken the Entity during the trial for the survivors to escape. Which, if you think about it, if the generators did NOT generate any light, would the gates would even be powered since the Entity is not weakened enough to have a loose grip on it's own world and have the exit gates opened?
This proves the following ;
The Entity is weak to light.
Part 5 - Final verdict and unanswered questions.
The weakness to the Entity is intense light.
Now that this has been said, I have to ask, does the unseen survivors from the Lore (Vigo, Alex and the rest) have figured this out and it is how they managed to alter the nightmare construct, aka the realm of the Entity itself?
It would make sense for them to activate as many generators as possible, and when they are all lit, would weaken the Entity enough for them to manage to create items or means of escape INSIDE the realm of the Entity. It would seem that the only circumstance when the Entity cannot fully control it's own realm is when it is filled with light. Which would then open the possibilities to make things appear that did not originate from the Entity itself...
Comments
For OP. I very much like this theory. It seems quite plausible. Of course, the devs tend to make the Lore up as they go along so I don't think they themselves have thought of that yet. It's a common practice to re-use assets like particle effects in the early days of a Game's life when it's not clear yet how successful it'll become and it would be worth spending time creating new effects or not.
At any rate, I'll ask the devs what they think of your theory, since I'd like to incorporate it on the Wiki.
This might be out of blue, but explaining illogical things with logic... does not always work
anyway, what if there are 2 entities, one which feeds on despair and creates trials where survivors are tormented and the other feeds on hope and provides gates, engines, exits and power to flashlights?
the problem with light theory: engines also shine light but killer don't see/feel any problem being near them. Be it Wraith or any other.
Well, it's not shined into their eyes.
I did try looking at the lamps
Not the purpose of those lights though.
I get the idea about having a map where the campfire lies... and after that change the lobby as another map... That would be cool.
Yes they may escape the trial, but they did not escaped the Entity's realm, so they are still prisoners. It's just a circular way to build and consume hope.
ay thanks Doc :^)
In lunar new year this spirit world effect could be seen around survivors, when they pick up the vessel. Maybe vessel represents some kind of energy of lost souls? Most likely, killers destroying them for the same reason.
Can someone please find a picture of this circuit box and post it?
I think I understand why the moon, atmospheric lights, those things, don’t blind or hinder the killers, but the flashlights do. There’s a reason why you can take items out of the trial. The very fact that Killers can be blinded proves that the Entity is unstoppable.
I read a book where a person was god in his house. He couldn’t be hurt, he couldn’t be defeated. He was super strong. At all logic, he should win everything. Only he died, because of a single weakness.>
The reason why the fire and other lights don’t burn the killers is because they’re tethered to the entity. It isn’t just light that burns them; it’s the survivors hope, the Hope combined with the light, that does it.
Survivors are in a nightmare, but they’re still alive, still breathing.
I like this theory, made me imagine how cool it'd be if you were in the spirit world as wraith, you could see the entity in part. idk if spirit world users can see each other at any one time though.
I always thought the Entity's weakness was tacos. 'Cause I mean, who could possibly resist?
This is very interesting. One thing I've always wondered is where do the survivors go to when they escape through the gate? Do they go back to the real world, or do they just find themselves forever trapped within this nightmarish world, just they're safe for the time being? Another question, what lies beyond those gates?
When survivors escape, they go back to the campfire. That's what lies beyond the gates.
mini-update : I added some images and gifs back since I realised they were missing for some reason.
So we just get Alan Wake up in here and we're all good, right?
@TheBretzel A thought crossed my mind after reading this. In the movie Hollow Man, it has Kevin Bacon's character turn invisible, much like the wraith, albit slower. The effects you describe from the wraith could simply be his internal parts becoming visible before his outermost skin and this comparison would also explain wraith's weakness to light, since invisible eyelids are worthless.
I really like this theory but since EGC just came out and your theory about how doing generators weakens the entity then what about EGC the entity demonstrates it's power when all gens are done there and doesn't appear to be weak if not stronger.
Easy! The Entity Actually doesn't spawn on the windows nor the exit gates.
The reason why you can't just shine the flashlight on it may because of 2 things
1) The Thing Blocking the Exit Gates and Windows are actually spawned bars. That the Entity spawned to prevent the survivor to escape or keep going through windows.
2) The reason why you cant just shine the light on it when it's about to kill a hooked survivor is because well... The entity spawned the flashlight in the first place. So, the flashlight can only be intense for the killers because the entity rewrites them (Like the Teachable Perks) So it's only bright to them because the entity made it to be, but that doesn't mean that the flashlight is so intense for the entity. So the entity made the flashlight low enough where it won't hurt the entity.
Ik #2 got confusing but to make things short the entity rewrote the killers to be impacted by non-intense light.
If Entity is vulnerable to light, same thing with her powers, as we can see with example of Wraith, Hag and Nurse, which was proven above. So, I call bullshit.
My only problem is that the Entity has clearly shown that at any time it can block the generators. If the entity has this power, why not always do it? The generators are made by the Entity as a means of generating hope. which we know for fact is what it feeds off. Same goes for the exit gates. If the survivors don't have a chance at escaping, then they have no hope, and thus no meal for the entity.
While the entity is weak to light, the light is controlled by the entity in it's realm. I would agree on perhaps the gens do allow for creation of items in the realm that offer a means of escape or the like, except that the hatch now always spawns, a means of escape that we confirmed was *not* under the entity's control, when a single survivor is left, no matter how strong or weak the entity is.
The entity creates everything via what is called auric cells (survivors have been known to collect and even manipulate these cells). I had a theory about the entity's true connection to these cells as it also says the entire trial is the entity, I feel these Cells respond to hope (which is why the entity feeds on hope, because it is one of these cells but not a normal one the entity is a queen auric cell (an intelligent one at that, giving rise to more and more AC from it's self). Auric cells are like a hive mind building block being controlled by the QAC (the entity) to take any shape necessary and it is the fact that auric cells are a hive mind that survivors can so easily manipulate them (Vigo litterally being able to make his/her own little hidey plane) just cut their connection with the queen and input your own directions (ie ensuring medkit in the first chest).
I just discovered this thread and read it while listening to the lunar new year theme (https://www.youtube.com/watch?v=CulxhrlPBsM) and I had real chills! That's an amazing theory. I love the lore in general, I can't wait for the archives to be released into the game so we get even more lore!
Adding to my post the manipulation of these cells could be why Vigo has evaded the entity so long as when the entity is near he could just turn the cells to his side (very dangerous to the entity if true) but as far as I know (and can anyone confirm) if Benedict knows how to manipulate them?
Benedict is thought to be dead or stuck in the void, where useless survivors and killers go.
Will we send GF there?
I personally wouldn't send him there. I'm not sure if I've just been meeting potatoes or if I'm absolutely god at GF, but I can get the ability to work most of the time, even with the bug.
Nice theory but there are some evident and non-negligible mistakes.
Point 4 especially (the generator's one), is completely wrong. Devs have confirmed multiple times in their streams (have done so in their latest lore-based stream too) that everything you see in the Trial is made by the Entity itself except for the Survivors and the Killers. The Gens, the Escape Doors and the Hatch are made by the Entity in order to give Survivors a chance at escaping and are not constructed by any survivor. Those thing are just a manifestation of the Entity itself just like everyhing else around the map. Without them Survivors would have no hope to ever escpae a Trial and with no hope comes no feeding for the Entity. So point 4 is completely wrong.
Items like Flashlights are also made by the Entity and given to the Survivors as a tool to increase their chance at surviving hence to increase the feeding the Entity can draw from them. So the Flashlight's light is also made by the Entity itself.
Nice theory but there are some evident and non-negligible mistakes.
Point 4 especially (the generator's one), is completely wrong. Devs have stated multiple times in their streams (have done so in their latest lore-based stream too) that everything you see in the Trial is made by the Entity excect for the Survivors and Killers. The Gens, the Exit Doors and the Hatch are made by the Entity itself to give the Survivors hope to actually escape, since we all know that no hope = no feeding the Entity can get. So those things are just a manifestation of the Entity like everything else in the Trail and are not construced by any survivor. So point 4 is completely wrong.
The Flashlights are also made by the Entity and given to the Survivors to increase their chances at surviving, their hope of survive the Trail and the feeding the Entity can draw from it, so the Flashlight's light is also made by the Entity itself.
I allways thought the entity weakness was stabbing the floor since the realms are made out of her
good theory tho
Nice theory! I like your take on it! 😁
Made of yes but specifically the auric cells that "form" its "body" at the time it is the trial you could argue that they aren't truly the entities body but an extension of
We’re of to kill the entity the horrible entity of death 😃
Hey Random but is it alright if I use this as a Video idea?
With the additions of killers like ghostface and myers(the shade), that can remove the red stain themselves. You could infer that they wouldn't be entirely controlled by the entity?
The only question I have is, if the other survivors created the black lock, then why does the black lock lead to darkness and not to light?
One thing I just remembered: There are fire barrels everywhere... why wouldn't a survivor take a stick and light it?
Correct me if i'm wrong but does it not seem like the entity is weak with the eyes only it and don't ya think. It also explains that the killer is the entity because the entity can't see from the survivor's eyes which is why the entity is blocking the window's only when you are in chase :D
The entity is not the killers already stated in the lore but good try tho
Thank you for correcting me
You are welcome
Figured I could bring up the fact that Hex perks produce light even though they help the killer. Seems to break the theme of light being the weakness when its directly aiding the killer giving them more power.
Bro