Per 
SCP - 5506 "I am you"
Object Class: Euclid
Special Containment Procedures: SCP-5506 is to be contained in a standard human containment cell, and provided with base human needs, such as food and drink. For the entity's health, it's cell must be cleaned biweekly, and all who enter must wear full-body military-grade hazmat suits to mask their appearance and avoid inhaling the gas produced by SCP-5506. Every person to enter and leave the cell must be accounted for.
Description: SCP-5506's natural state appears to be an amorphous mass of unknown gas, henceforth identified as SCP-5506-1. Testing has provided inconsistent results, so it's theorised that it is a mix of several gases such as ammonia, hydrogen peroxide, carbon monoxide and water vapour, although this has yet to be proven definitively. What is known however is that infrared scans have shown SCP-5506 to be a humanoid entity beneath the gas, and all attempts to manually extract the gas have failed (See testing log 5506-1).
SCP-5506-1 is highly toxic when inhaled, and all subjects who have done so died at inconsistent times, ranging from 30 seconds to 24 hours. Interestingly, however, this only has the affect on mammals, as lizards, birds, plants and insects seem immune to this property. Further testing on the reasoning for this is awaiting O5 approval.
Not only is the gas anomalous, which would be problem enough, but SCP-5506 is capable of dispelling this gas to reveal itself, when revealed it is always taking on the form of someone it has seen personally in the past. Photos and videos do not seem to have the same affect. For this reason it is strictly forbidden any future interaction be made with SCP-5506 unless their appearance is fully concealed.
SCP-5506 itself is roughly 189 cm tall in it's default state, which has been proven using infrared cameras and electronic tape measures. It weighs only 100g, yet medical tests show that it should weigh as much as an average american male. It is suspected SCP-5506-1 is somehow lifting SCP-5506 enough to make it seem lighter, yet still keeping it on the ground. Once again, Further testing is awaiting O5 approval.
Date Obtained: ██/██/2020
SCP-5506 came into the attention when a cloud-like entity was reported wandering the streets of Berlin, Germany. It is unknown how the entity avoided the attention of the foundation for so long, since it claims it has existed for a long time, however it could not specify an exact timeframe. SCP-5506 was surprisingly cooperative, handing itself over to foundation staff almost immediately after it knew it had been discovered.
Testing Log 5506-1
Subjects: SCP-5506 and SCP-5506-1
Time: June 34, 20██, 5:30am
Test: Using a vacuum connected to an airtight cell containing SCP-5506, attempt to extract SCP-5506-1.
Results: After 7 hours of the vacuum extracting SCP-5506-1, SCP-5506 didn't seem to have any less of the gas around it, and when the vacuum was turned off SCP-5506-1 seemed to retreat back into SCP-5506. It seems SCP-5506 is in some way physically connected to this gas, or at least capable of controlling its flow.
Notes: So not only is this gas deadly and unidentifiable, but we have no way of removing it? Further testing has been requested. - Dr. █████
Testing Log 5506-2
Subjects: SCP 5506-1 and one adult male Red Factor Canary
Time: September 2, 20██, 12:30pm
Test: Expose subject to SCP-5506-1 for one full minute. after exposure, remove, isolate and monitor for 24 hours.
Results: The canary seems to become aggressive when it sees SCP-5506, but otherwise showed no effects when exposed to SCP-5506-1.
Notes: Interesting, I will propose the usage of SCP-5506-1 to protect endangered animals. We will however need to test the effects of SCP-5506-1 being isolated from SCP-5506.
Testing Log 5506-3
Subjects: SCP-5506 and SCP-5506-1
Time: September 15, 20██, 10:15am
Test: Using an airtight container, seperate a small amount of SCP-5506-1 from SCP-5506
Results: Approximately 5 minutes after seperation, SCP-5506-1 breaks through the airtight container, returning to SCP-5506
Notes: Damn, guess that proposal from earlier this month is denied
Interview Log 5506-1
Interviewee: SCP-5506
Interviewer: Dr █████
Foreword: Dr █████ is wearing a military-grade gas mask, but is otherwise easily identifiable. Accompanying him is D-████ and an armed guard wearing full-body armour.<Begin Log>
Dr █████: Hello SCP-5506
(SCP-5506 immediately disperses SCP-5506-1 and looks to resemble Dr █████)
SCP-5506: Hello, Dr █████
Dr █████: How do you know my name?
SCP-5506: I know everything about you, Dr ███████ █████. After all, am I not you?
Dr █████: We are aware of your properties, you aren't fooling anyone. For the sake of this interview and our research, I advise you remain professional and avoid any acts of hostility or trickery.
SCP-5506: Why, I would never act hostile towards an esteemed man such as yourself. Might I say you have a rather interesting life, a straight-A student! You clearly had it all figured out.
Dr █████: SCP-5506 please refrain from revealing personal information unless instructed otherwise. any further breaches of this will be omitted.
SCP-5506: Fine, Dr █████. So, you're here to ask me questions about myself, my past, all that stuff. I'll humour you and let you ask them, instead of just answering them now.
Dr █████: That would be best. Now, state your name.
SCP-5506: You know, I don't actually know. I suppose now I'm Dr ████████ █████, or as you call me, SCP-5506, but I don't seem to be able to recall my initial name.
Dr █████: Very well, how long have you existed?
SCP-5506: Once again, I couldn't tell you. It's been oh so long, I'm afraid I've lost track of time, but I do recall it being my birthday yesterday. It's such a shame too, nobody came to speak to me.
Dr █████: Even if we were aware of such an event, it is not an event to be celebrated, especially not here. Moving on, what gas is SCP-5506-1? Our tests proved inconsistent.
SCP-5506: Again with the difficult questions! Doctor, if you were to ask something easier such as "What's 2+2" or "What is my favourite colour" I could easily tell you that is is 4 and your favourite colour is teal blue, but alas you ask me the difficult ones. I'm afraid I don't know the gas, although I know it's somewhat common here on earth.
Dr █████: Alright, well let's try something else, how would you describe your abilities?
SCP-5506: Ah, now that I can answer. I suppose it's a sort of shapeshifting, provided the shape that was being shifted was my identity. In a sense, I become you, or whoever I choose.
Dr █████: Thank you, now would you be able to describe your normal appearance?
SCP-5506: How could I? Surely you have noticed I'm always covered in that gas when I'm not taking on the identity of someone, so you can imagine how difficult mirrors are. For all I know I might not even be humanoid!
Dr █████: That's… disappointing. Could you shapeshift into this D class here?
SCP-5506: Easily, provided you all leave first, call it performance anxiety, if you will.
(Dr █████ leaves the room alongside D-████ and the armed guard. while they are out of SCP-5506's sight, D-████ is terminated. One minute later they return without D-████. SCP-5506 has not changed it's appearance)
SCP-5506: I know what you're thinking, and I can explain.
Dr █████: Very well, explain. Why aren't you resembling D-████?
SCP-5506: Well, I was trying to, but for some reason I just forgot what they look like! I swear this never happens, usually I can remember a face for years!
Dr █████: Thank you for trying. This interview will now end.
<End Log>
Ending Statement: It seems SCP-5506 is suffering from severe retrograde amnesia, as well as a loss of identity. Furthermore, SCP-5506 is unable to remember someone who is deceased. It is possible SCP-5506 could be used to learn the condition someone is in, provided they have been seen by the entity, but the potential risks of this to both SCP-5506's psyche as well as the privacy of the subject are unknown as of now.
Interview Log 5506-2
Interviewee: SCP-5506
Interviewer: SCP-5506
Foreword: SCP-5506 was seen talking to itself in the corner of its cell through one of the installed cameras. As a result, this interview lacks professionalism, but could allow us to get a better understanding of SCP-5506's psychological state. Furthermore, to avoid confusion, we will refer to both sides of the interview as SCP-5506-A and SCP-5506-B.<Begin Log>
SCP-5506-A: Who are you?
SCP-5506-B: I-I… I don't know, I don't know who I am.
SCP-5506-A: How do you not know who you are?
SCP-5506-B: I don't… I don't remember, I can't remember anything
SCP-5506-A: But you must, surely it's in there somewhere
SCP-5506-B: No… No it isn't, It's gone…
(Infrared cameras indicate SCP-5506 scratches its scalp furiously)
SCP-5506-A: God damn it pull it together! You're supposed to have control over your identity, not lose it!
SCP-5506-B: I can't help it! I don't know why this happened, I don't know why I'm like this!
(SCP-5506 proceeds to rock itself back and forth, muttering comforting thoughts to itself, as well as apologising)
<End Log>
Ending Notes: SCP-5506 may be developing a split personality alongside severe anxiety as a result of its condition. Further testing is forbidden to prevent further psychological damage
