Specimen 7 appears to be a large, moving, red-and-black wall of distorted images that resemble skeletons and corpses.
Upon entering the door, the player sees themself in a flesh-like hallway. After exiting this hallway, Specimen 7 will start chasing them. From that point on, the player must run through a series of twisted corridors with shifting images along the walls, created by the player's mind under the influence of Specimen 7.
Though slow, Specimen 7 kills the player instantly on contact.
CAT-DOS states that it is "only effective on subjects with a past trauma or mental issues".
"STRANGE WIGGLES", Specimen 7's chase theme.
- Rarely, Specimen 7 can turn into a normal wall.
- Sometimes, the Rooms which Specimen 7 "corrupted" can be very glitchy (e.g. transparent walls).
- Rarely, other Specimens may appear alongside Specimen 7 during the chase.
- The Cat's relation to Specimen 7 is unknown; for some time, the cat was suspected to be Specimen 7 itself, and may indeed be a part or a consequence of its existence, sort of like a psychic Good Cop/Bad Cop.
- Since The Cat references archetypes from Jungian Psychology, the Cat's role might be akin to a therapist, with Specimen 7 being the trauma being treated. Considering the last piece of advice The Cat gives the player is "Knowing your shadow can greatly help you, but be ready to see what you'd rather not be", it's possible that Specimen 7 is a manifestation of the Player Character's shadow archetype, or is related to it.
- Specimen 7 is visually similar to Giygas's final form from Earthbound (or Mother 2) while its behavior may be a reference to a similar mind-world flesh wall chase from Penumbra: Black Plague.
- In the 2.5 update, the player no longer stays in Room 410 for the duration of the chase: it now progresses.
- Specimen 7 doesn't have a death screen, along with Specimen 3.
- Specimen 7 can be encountered one time only, along with Specimen 13.
- It is one of three specimens that can instantly kill the player on contact, the others being Specimen 9 and Specimen 12 while in the Mansion.
- The art for Specimen 7 is recycled from another project Akuma Kira was working on.
- Bizarrely, it seems other Specimen can spawn and begin to chase the player in the Flesh Hallway right before Specimen 7 spawns, meaning that, if one is "lucky" enough, they can be chased by two Specimen at the same time, as shown in the gallery.
- Specimen 7, along with Specimen 13, are the only two specimens from the original game not found in Endless Mode.
- Specimen 7 may also be a reference to the Wall of Flesh, from the popular action-adventure sandbox game Terraria.
Unlike the original game, the specimen is 10 degrees inclined.
The rooms during the chase became a bit darker than the original game.