There exists in The Sanctuary a single mirror. It is never found in the same place twice, and it does not rest in any given spot for long. Its appearance is fluid, changing for each traveller it manifests before, a detail that may seem irrelevant or unnecessary. It is not. I mention the fact only to prove just how intimately the mirror knows you; after all, the reflection you cast is so much deeper than the one you see.

When travelling in a group, or with at least one other individual, the mirror will not appear. Self-contemplation and existential questioning are private activities, and are often hindered by the distracting qualities of those around us. As such, it targets those in isolation, in prolonged solitude, who are starved for interaction and drowning in their own consciences. The weaker you find your composure and will to persevere, the more malleable you are to The Sanctuary, and the more likely you are to be preyed upon by the Alternate. Consider it an inter-dimensional alliance: both entities win if you step through the glass.

The Alternate is a child of The Sanctuary, but it is unique amongst its kind. Giving it what it wants, regardless of how far one goes, allows the being to mark its victims. It takes a special interest in these individuals, learning more about them with every encounter it creates. And, should a survivor be one of the very few who manage to leave The Sanctuary on their own accord, it has the strange capacity to follow them on the trip between worlds. Do not let the Alternate mark you. Regardless of your fate, it will only grow more persistent with time, and it will show you things you do not want to see: personal and haunting truths that hover above the understanding of humankind, only becoming more brutal and devastating with every second you put between yourself and this marvelous nightmare of a reality.

To allow maximal clarity in my warnings, I will preface my descriptions of the Alternate with this repeated warning: everything I am about to disclose, every example or hypothetical experience I propose, will only be exponentially worse should you doom yourself to irregular but unrelenting mirror-bound visitations for the remainder of your existence. Read carefully, act with caution, and you should escape unscathed. More or less.

It would be incorrect to describe the Alternate as a person, and equally diminishing to categorize it as a limited plane of reality. It is somehow both and neither, a mere infant hoping to follow in the footsteps of the torturous dimension that gave it life. In the matter of your simple comprehensive capacity however, it would be easiest to differentiate the entity into two sub-components: the realm of The Alternate, and the shape-shifting humanoid that lives within.

The mirror is the doorway between worlds. Glass is fragile, weak, flexible, and acts as the perfect border from one beautiful hellscape to the next. Do not touch the glass. When encountering the Alternate, you do have a chance of remaining unmarked and unharmed; this disappears if you come into physical contact with the mirror's surface. Avoid this at all costs.

At first, everything will appear normal. Or rather, it will appear as normal as anything can in The Sanctuary, where the word is typically undefined. The mirror will materialize from nothingness, having decided upon you as an easy target, and by extension, its next victim. I do hope it is a foolish choice.

Some survivors describe it as ornate, an intricate wooden frame outlining their cursed reflection. Others refer to its modern style, frameless and held up by a single silver rod. I've already mentioned that its appearance changes for each attack on its vulnerable human prey, but this will not come as a shock due to one key detail. The Alternate already knows your name.

As far as the oral tradition of storytelling can be verified, it does not like to follow patterns in this matter either. One traveller says it was woven into the very shape of the wooden header, others claiming it was traced into the hints of steam and condensation that remained on the cool glass. By far the most haunting, however, is the account in which someone found their name scrawled across the mirror in blood, with the uncanny and inexplicable knowledge that it was their own. The Alternate is not bound to this level of space and time, and as such does not abide by the rules set forth by The Sanctuary. It splits its presence between this world and the one of humanity, making it a sort of traveller too. Yet it has an alliance with the monsters that lurk in the shadows.

This is all to say that the Alternate knows you, perhaps even better than you know yourself. There is always room to learn, and it will do just that should it be given the chance, but until then it only wants to make your acquaintance. It knows your name, but it will not offer it to The Sanctuary. If you acknowledge it verbally in any way, you are sacrificing your own identity. The Alternate is not responsible for any impulsive naivety. It is just here to meet you.

Step closer. You will know when you've entered its domain. The entrance to The Alternate is distinctly different from the deceptive peace of The Sanctuary. It is all about first impressions, and it wouldn't dare give you a fake one. Of course, as is usually the case with these stationary threats, it is pointless to run. The Alternate has already chosen you. It will follow you for as long as it takes.

Try not to be alarmed when the shift occurs. The world will grow dim, the earth becoming a charred black as red veins twist and writhe, seeping slowly outwards from the base of the mirror. The glass itself will radiate light, a subtle but persistent glow that will call you towards it. Resist. You will be greeted soon anyways, and there is no need to put any less distance between yourself and the entry point. You are close enough.

Eventually, the Alternate will decide to show its face. You might recognize it. After all, it is your own.

It is difficult to describe where the reflection differs from the source, and yet it somehow always does. Of course, it will likely have been a while since you last studied your own image, but the dirt and weariness of time are not the surprising part of the Alternate's portrayal. In any regular mirror, one's visage would carry their personality, their flaws, their spirit. The Alternate does not. It is not like you, and it does not have any of those things. It is a creature of darkness, an emotionless ghost of the psyche, and most importantly of all, it is not human. This will become clear when it looks you in the eye; even the uninformed become strikingly aware of the otherness it possesses.

If you are unlucky, it will speak to you. The voice it uses will resemble your own, and yet it will be unlike anything you have ever heard. It may try to persuade you to inch closer, or it may simply launch into unnervingly polite small talk. Try to give as little detail as possible, but unlike in the past, do not lie. The Alternate does not ask questions it does not already know the answer to, and it does not favour those who put their fate in deception. Unfortunately, if it has chosen to speak, your mission is that of mitigation. The being has taken a profound interest in your existence, and you have been marked before you even had a chance to defend yourself. But do not allow this to mute your awareness of the situation; the outcome may have been decided, yet your life is still hanging in limbo. You do not want to leave it there. Not with the Alternate.

As sealed as this possibility is, some travellers have insisted that an inevitable marking is much preferred to the cold, steely silence of the Alternate's glare. It will not smile, move, or even blink; it will only watch. And just as the power structures of The Sanctuary do not apply under the Alternate's reign, neither does time. It will never grow impatient, and it will never look away. The human mind, while fragile and inefficient, is fascinating under pressure, and it would like to see you break. Just as you've practiced thus far, try to remain calm. This is not an easy task after extended periods of isolation or emotional ruin, but shattering your composure gives the Alternate everything it needs. It will start to talk, and it will offer you solutions to your unsolvable problems: they'll just be waiting on the other side of the glass. All you have to do is walk through it. This would be a grave mistake.

If you manage to outlast the Alternate's lengthy but evidently limited attention span, it will decide that you are not interesting enough. Similarly to The Sanctuary using a test to determine your competency, the Alternate makes these decisions by itself, trying to weigh its options before making the irreversible choice. In this test however, you do not want to pass. You would not have survived to see the outside of the Hostess' dusty house had you not proven a worthy playmate for the larger deity, but now you must give the Alternate no reason to dote upon you. When the red tendrils begin to retract, you will know you have succeeded. If they continue to burrow towards you, acutely alive in a world in which everything is dead, then the test is not over. It will only ever end one of two ways: the Alternate will excuse itself, or you will step into the mirror.

The mark of the Alternate is a curse, but it is not the final destiny of its victims. Even without the option of silence, there is still hope for you to survive the encounter. It is a mere matter of willpower and inner strength; the only procedure is to stay where you are. Perhaps it would help if I described what awaits on the other side of the reflective portal. Sometimes knowledge is the greatest deterrent.

The world that calls you is eldritch and unknown. It does not aim to disguise itself as friendly and familiar, and even as you step through the entryway, the one recognizable anchor you have will disappear. The Alternate's true form does not resemble you, or any other human being for that matter. Its face is gruesome, its body twisted and broken, its presence even more overbearing and terrorizing than before. If you do end up in its realm, I have only one piece of advice for you: avoid the Alternate's physical form as much as possible. The fate that awaits you is tragic enough without losing a piece of your psyche in the process, though you may have differing opinions on the subject.

It is also important to note that there is no leaving The Alternate. The mirror is a one way door, and there is absolutely no escape from the hell it hides. We do have evidence of an exit in The Sanctuary, in the tales of ancient visitors and the twisted logic ingrained in the very nature of this dimension. And while we have no idea where it is, or what form it takes, we know it exists. This is a luxury the inhabitants of The Alternate do not have. There is no escape; not even the bittersweet arrival of death. Everyone is immortal in The Alternate. How unfortunate.

The other victims will be no use to you beyond the glass. They will not fill the silence with conversation, or even attempt to build a meaningful relationship, the likes of which every inhabitant once so desperately craved. You will never even know if this could have been a possibility in another realm, or another time. For in the dark, featureless expanses of The Alternate, where the only colour and light are the red glow surrounding the territorial and menacing ruler, the human senses find themselves at a breaking point. After a few minutes, you will not be able to see anything other than the colours of blood red and nothingness; a few hours and you will find yourself unable to hear; a few days and suddenly you cannot speak. You will wander around aimlessly for all eternity, alone with your own thoughts and growing tired with every passing moment. You will have nothing but time for self-reflection, until even the idea of identity makes you sick. And most importantly, you will be alone. Forever.

Do not step through the glass. The Sanctuary is a nightmare unlike any other, but it is fair and complicated. The Alternate is neither: there is no chance of escape, no opportunities for comradery or moments of success. There is only you and your thoughts, watched over by the indescribable being that slowly drains the individuality from your soul. It does not matter if you have been marked or not, if you follow its call beyond the mirror.

As for the Alternate's mark, I do not mean to put insufficient emphasis on the horror of its effects. It is preferable to an infinite lifetime in its domain, of course, but it should still be avoided to the very best of your ability. You do not want to be marked. Maintain your composure, and you will be fine. Snap, or allow the Alternate to take a special interest in you, and you will be followed for the rest of your natural life. The mirror will continue to appear before you in The Sanctuary, visible only to you, a song of loneliness and an eerie duplicacy. Should you be fortunate enough to somehow return home from this fear-riddled masterpiece of interstellar torture, the Alternate will instead appear in the mirrors of everyday life: in the one on your bathroom wall, the reflection of a puddle after a rainy day or the car window as the light shines on the thin glass. It has you in its hands and it will never let you go. The Alternate wants to know you, and what better way is there than to watch as you move on from the most traumatic experience of your life?

Yet relationships are formed between two individuals, and so as the Alternate gets to know you, it will slowly start to reveal its true self as well. And somehow, you will still see yourself in its monstrous reflection.