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(Draft for SCP-3561. Still need to create an incident log, not sure what the correct format for that is.)
Item #: SCP-3561

Object Class: Euclid

Special Containment Procedures: Containment of SCP-3561 in its entirety would be implausible for the Foundation. Instead, a one kilometer perimeter is to be maintained around SCP-3561-A, preventing access to the area. A task force equipped with sealed equpment and filtermask will remain stationed on site. Once a week, the task force will sweep the containment zone, terminating any instances of SCP-3561-B discovered. Tissue samples should be collected from each specimen, and sent back to the on-site lab for analysis.

Description: SCP-3561 is a large organism located in ██████, West Virginia. It exists inside a single cave system located within the Appalachian Mountains. consisting of a black material found to be similar to mycellium in fungus. This material is also theorized to subsist off minerals present in the cave's wall, as well as geothermal energy present in the area.
It is currently unknown how far SCP-3561 extends, but it only connects to the surface at one cave opening, SCP-3561-A. Studies, however, have indicated that SCP-3561 occupies a large area of caverns, and is currently in a phase of growth. The cavern has only recently opened to surface access, approximately ██ years ago.

SCP-3561 is known to create instances of SCP-3561-A as well. These are humanoid figures, composed largely of the same mycellium found in SCP-3561. Instances of SCP-3561-B are typically capable of movement at rates similar to an average human, and in some cases even speech [see Incident Log #46]. They exhibit basic intelligence, and tend to cooperate extremely well, suggesting the existence of a combined cognitive center. Instances of SCP-3561-B attempt to emerge from SCP-3561-A at seemingly random lengths of time, ranging from █ to ███ days. During this process, a group of SCP-3561-B composed of less than a dozen individuals will exit SCP-3561-A, moving into the surrounding forest. These groups will spend a short period exploring the area surrounding SCP-3561-A, before attempting to breach containment. Subjects will become curious if alerted to human presence, attempting to physically make contact with humans. If contact is made, the instance of SCP-3561-B will immediately move back toward SCP-3561-A. If the instance successfully returns, it will descend into SCP-3561-A, disappearing inside. The human victim will exhibit delirium, and protrusion of fungal tissue from bodily orifices in the form of black mushrooms, similar to those of the genus Cordyceps. Afflicted individuals will eventually become covered in this material unless terminated before █ hours pass. After this period, all human life signs will have ceased, and the victim will become another instance of SCP-3561-B. If the instance successfully returns, it will descend into SCP-3561-A, disappearing.
If a contacted instance of SCP-3561-B returns to SCP-3561, further generations of SCP-3561-B will exhibit changes in morphology. These changes vary drastically in each event, but each one causes SCP-3561-B to display more humanoid traits, inclusing the development of a quadrupedal body, facial features, increased aggresiveness and curiosity, and the ability to speak. Changes made by contact are permanent, and affect all future instances. Thus, this event should be avoided at all costs, to precent increased risk of a containment breach.

Initial observances of SCP-3561-B displayed behavior characteristic of innocent curiosity. Instances of SCP-3561-B present during the transformation of afflicted humans displayed signs of distress, attempting to flee. However, as individual instances returned to SCP-3561-A after encounters with Foundation agents, more guarded, cautious behavior arose. Instances eventually developed hostile defensive behavior, actively attacking agents to facilitate escape attempts.