Special Containment Procedures: SCP-7121 is currently uncontained and believed uncontainable. However, development of the following containment protocols has rendered the risk of containment breach minimal.
At the exact start of every new moon (approximately 29.5 days), one D-Class personnel must be locked in a standard large biological entity containment unit and be made to say the summoning phrase. Confirmation of abduction of the D-Class personnel should be confirmed afterwards by two direct eye-witnesses. No cameras should be present in the containment chamber at any point.
Under these guidelines, a containment breach would constitute a failure for a Foundation-authorized personnel to be the first person to the speak the summoning phrase in any given lunar month. Given the entity's nature, a member of the public accidentally summoning SCP-7121 is generally a self-resolving issue, but mention of potential SCP-7121 sightings online are to be flagged and removed by Foundation web-crawlers, and all confirmed direct witnesses apprehended for questioning and amnesticization.
Description: SCP-7121 collectively refers to two interconnected anomalous items. SCP-7121-1 is a large, predatory creature that can be summoned once per lunar month1 by a living being speaking aloud the phrase, "Come, the pale wind's hound."2 SCP-7121-2 is an extradimensional realm of unclear bounds, which can only be accessed through SCP-7121-1.
SCP-7121-1
SCP-7121-1 Description: SCP-7121-1 is approximately 7 meters long, quadrupedal, and displays similarities to troglobitic organisms. Subject has pale skin, and a thin and bony head without visible ears or eyes, though what appear to be vestigial eye sockets are present. Each of its four limbs end in four-fingered claws, with the front limbs additionally possessing a fifth, opposable digit. It possesses four prehensile, tendril-like tails which can operate independently, but typically are kept furled together. Subject's mouth, which can stretch up to 1 meter wide, is surrounded by 12 tentacular appendages which form a loose beak-like shape. It displays a clear preference for humans as prey items, though it has been observed preying on other creatures.
Additionally, SCP-7121-1 can phase through all forms of physical matter, becoming selectively immaterial, and can extend this effect to objects it is in contact with, though the exact limits of this ability are unclear. Though prey will generally be swallowed intact, if provoked or angered it will use its phasing ability to pass its claws inside a victim before making them solid again, resulting in a debilitating and often untreatable wound.
The first time the summoning phrase is said after a new moon3, SCP-7121-1 will be summoned to the speaker's location, usually through the floor or a nearby wall. This has, in nearly every case (see addendum SCP-7121.4), resulted in it consuming the speaker and anyone else who enters the area around the speaker before disappearing into the nearest solid surface. Attempts to track its movements after disappearing into a surface have all failed, with tracking devices quickly ceasing function. This process will fail and SCP-7121-1 will not appear if the speaker is currently being observed through any means. Subject can be recorded or photographed with relative ease, but doing so is discouraged as it appears to anger it, causing it to act more aggressively and typically results in damage to personnel and equipment.
SCP-7121-2 Description: Once SCP-7121-1 disappears into a solid surface and outside of observable distance, consumed prey items will be translocated to SCP-7121-2. The appearance and landscape of SCP-7121-2 has varied in each experiment while maintaining consistent similarities, typically being a foggy landscape, with items that will generally feel familiar or significant to those witnessing them scattered across the environment. Persons transported to SCP-7121-2 typically find their clothing and carried equipment altered, often into entirely different items, with no correlation determined between the original and transfigured items. Subjects generally describe the alterations as feeling appropriate for them, suggesting a correlation with the subject's self-image.
Common characteristics of SCP-7121-2 include sparse plant life, an overcast night sky, thick fog that somewhat limits visibility, and stagnant water that reaches up to at least knee level (regardless of the height of the subject). There have never been any lifeforms discovered in SCP-7121-2, but transported subjects have noted the presence of "ghosts", described as static voids shaped like three-dimensional human silhouettes. Viewers have described a sense of unease and discomfort upon witnessing these figures, and they may possess an anomalous ability which prevents occupants of SCP-7121-2 from interacting with them, as in all experiments subjects have refused to do so.
There is no known means of escape from SCP-7121-2, and anyone transported to it invariably expires within minutes of entering from unknown causes, possibly due to the atmospheric content.
Addendum 7121.1: Discovery
SCP-7121 came into Foundation awareness on 2/24/20██ following a search of the abandoned ███████, NC home of Iurie Diacov, since designated PoI-2246. A note containing the summoning phrase was found along with a number of other anomalous items.4 Upon discovering the note, Agent Marai spoke the summoning phrase aloud to call a fellow researcher's attention to it, was abducted by SCP-7121-1 moments afterwards, and is now presumed deceased.
Addendum 7121.2: Test Log Audio Transcripts
Experimentation of SCP-7121 was authorized after the abduction of Agent Marai, but it was not until test #14, where D-76553 was fitted with a long-range two-way radio, that SCP-7121-2 was discovered.
Addendum 7121.3: Exploration Log Audio Transcripts
Further explorations of SCP-7121-2 were authorized following its discovery in order to discern if recovery of SCP-7121-1 victims was possible, which would greatly reduce the expenditure of D-Class personnel. For expedition SCP-7121-I, two D-Class personnel were requisitioned, and informed beforehand about SCP-7121-1's appearance and the methods by which they would be accessing SCP-7121-2.
Addendum 7121.4: Incident Log Audio Transcripts
On 06/██/20██, the following incident was recorded during routine upkeep of SCP-7121's containment protocols.
Notes: The search for D-99541 is ongoing, but his location has not been conclusively determined. On 08/08/20██, D-99541's tracking beacon briefly resumed transmission, displaying the location as -██.██████, -███.█████ for 23 minutes before ceasing. Investigation into the location is ongoing, and the capture and interrogation of D-99541 has been designated Alpha-level priority for all staff assigned to SCP-7121.