Item #: SCP-5507
Object Class: Entos1
Special Containment Procedures: Due to its nature, SCP-5507 is effectively self-containing and is unable to impact reality. However, as the origin of its anomalous manifestation is unknown, it still poses a level of risk, and all personnel are advised to be cautious when experimenting with SCP-5507's metaphysics.
Description: SCP-5507's only defining characteristic2 is that of its SCP designation. In other words, SCP-5507 is only SCP-5507, displaying no other defining traits or signs of its existence. This identity of SCP-5507 is rigid, preventing other anomalies from being classified as such. It is theorized that SCP-5507 would functionally cease to exist if its classification were somehow revoked.
As a result of this, SCP-5507 does not intersect with any known plane of reality, making the nature of its existence unclear.
Discovery: SCP-5507's anomalous attributes were discovered on 01/██/2020 following the opening of Series VI, when researchers at Site-20 found themselves unable to classify an anomaly as SCP-5507. It is unknown when SCP-5507 had its 'pataphysical awakening, though it is believed to be either:

The introduction of Series VI slots into viable contention (12/21/2019)
The creation of SCP designations as a way of labeling anomalies (█/█/18██)
The pataphysical creation of labels as identifiers (unknown)

Addendum 5507-1 - An Explanation of SCP-5507 by Foundation ‘Pataphysics Researcher Dr. O. Malloy:

If you don't completely understand what SCP-5507 is yet, don't worry. It's quite hard to define it using a completely formal tone. I am placing this document here in order to provide a more in-depth explanation regarding the nature of SCP-5507 in a more straight-forward way.
First thing's first, SCP-5507 is an entire entity. If it was just an inaccessible slot, then it wouldn't be 'pataphysical. Not only is SCP-5507 this entity, but this entity is SCP-5507. For most SCPs, the -XXXX designation is just a way of efficiently ordering it; you wouldn't consider it crucial to its identity. This is not the case for SCP-5507.
Another common misconception about SCP-5507 relates to an object and its reference. An object is the physical (or not-so-physical) 'thing' that exists, while a reference is how we refer to the object, be it semantically or otherwise. The actual rug is the object, the word 'rug' is the reference. Some believe that, for SCP-5507, the SCP-5507 designation is both the object and the reference. This would mean a constant loop of designating upon designations, which would be a metaphysical nightmare.
This is not the case. The object and the reference are completely seperate here; it's just that the object's only trait is that of its reference. It's a null object. Think of programming; we construct different classes (object), each with its own methods (traits). Humans can eat, walk, etcetera. Now imagine an object whose only method is being called by its reference, and nothing else. That's what SCP-5507 is.
For a more scientific definition of SCP-5507's location in the “Pata-verse”, we first have to define the term “Planes of Reality”, a term derived from study of SCP-3812, SCP-1304 and [DATA EXPUNGED], along with several other items. A plane of reality is not equivalent to a universe - some planes may contain several universes or perhaps several multiverses. Planes of reality exist on several levels, with each level containing potentially billions of these planes, growing exponentially the lower we go. For reference, we define our level as Level 0.
SCP-5507 does indeed not exist on any of these fully-defined levels. So then how does it exist at all? Well, our current best theory is that the SCP Database acts as a level in between levels - a Level -0.5, if you will. The reason it isn't Level -1 is that the database is not meant to exist as a completely new universe/narrative, but due to some way reality works, it still ended up detached from our world.
Additionally, just because SCP-5507's sole defining trait is being SCP-5507 doesn't mean that's it's only trait. To illustrate this, I will be using booleans (AND, OR, NOT), as even though they are not metaphysics, they are still a useful tool.
Is it true that SCP-5507 is, say, a piece of birchwood? No, of course. But that doesn't mean that it is not not a piece of birchwood too. Another common misconception about SCP-5507 is that not only is it not something, but it is also not not something as well. In other words, they believe that SCP-5507 exists unrelated to this birchwood-not birchwood dichotomy. If this birchwood problem was shown on a Venn Diagram, they believe SCP-5507 would be outside both being birchwood and not being birchwood, which would be worrisome as those probabilities equal 1 - a certainty. Luckily, SCP-5507 is not this complex - aside from its 'pataphysical abnormality, SCP-5507 behaves similarly to other entities, metaphysically speaking.
Do note, however, that SCP-5507 not being something (or any of the other traits, like being able to be tested on) is simply an extension of SCP-5507's defining characteristic.

Addendum 5507-2 - Testing:
Following use of a(n) [REDACTED], Dr. Malloy was able to test SCP-2719 on SCP-5507 in order to observe it's reaction to physical attributes. Prior to this, Dr. Malloy's home had become the ‘inside'.

Pointer
Outcome

SCP-5507
null

This test shows that SCP-5507 is able to be tested on.
Being outside or inside something is more-so of a physical attribute. In this context, SCP-5507 is neither inside nor outside, because it doesn't exist in that space. Of course, SCP-2719 has been tested on concepts with success, so I suggest that we test SCP-5507 with that next. - Dr. Malloy
In the next test, the ‘inside' was the concept of transformation.

Pointer
Outcome

SCP-5507
null

It appears that SCP-5507 does not exist on a conceptual level either. - Dr. Malloy
Addendum 5507-3 - Excerpt from Characteristics and Their Relation with Existence by Senior Researcher Dr. Koschov ███ (9/17/20██):

In the past few years, the Foundation's understanding of the pataphysical nature of existence has come to focus on the idea that an entity's attributes are a crucial part in how they not only continue to ‘be', but also how they function. For example, if you are a human, then you have all of the functions that a human would have. If you are a bird, then you have the functions that come under what a bird would have.
However, the last couple of months have brought upon a startling realization. While for a long time we believed that all entities had the underlying trait of simply existing, following the results of [REDACTED], it seems that is not the case. The only thing keeping us from slipping off of the face of existence is our character, who we are - specifically our broad strokes traits, like species, location, etc. Luckily, we have many defining characteristics that make falling off unlikely.
Unfortunately, also in recent times, we now know of several anomalies capable of reconfiguring a person's entire identity, personality, and overall metaphysical existence to a great degree. Due to our reliance on several defining characteristics, it is believed that a transformation of this degree would be metaphysically fatal. While a person's physical body and brain may still be there, their previous ‘self' wouldn't. In truth, are you really the same person as you were when you were younger? If a retroactive anomaly wiped all records of your past actions, did they still happen?
…
It is unknown what happens to entities when they cease to exist. It wouldn't be the afterlife, as that isn't even out of our plane of existence, much less the ‘'Pata-verse'. Nor would it be [REDACTED], as that is still within ‘being'.
…
One question I have gotten is that if non-existence denies everything, then wouldn't it also deny itself? This is a great question… (cont.)

Footnotes
1. Object is contained via its database file.
2. characteristic (noun, metaphysics): A trait that is fundamental to the identity of an entity or a group of entities. Describing items as what they are not is not a defining characteristic.

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