Unknown Specimen 4 (A.K.A. Tirsiak) is one of the specimens encountered in the Endless Mode.
Unknown Specimen 4 is one of the more human-like specimens in the game, and resembles a young woman with amber-colored eyes and short white hair which obscures her right eye. She also has the ears and tail of a wolf, which are the same color as her hair. She has a pair of brown deer antlers which seem to have a wooden texture, and a necklace with various gold beads on it. She wears a brown top with a shawl and skirt both made of dark brown fur, brown arm warmers lined with cream colored fur, and brown leggings with a band tied around the right knee. She is also barefoot.
Unknown Specimen 4's arrival is marked by blue mist throughout the rooms, and the silhouettes of wild animals (specifically, moose, bears and wolves) which will appear to block the player's path. The animals must be destroyed with the Axe to get past them.
Unknown Specimen 4 will do about 30 damage upon contact. She goes through walls and obstacles, and is unaffected by the axe and the sword. Whenever she damages the player, she will float backwards.
If she depletes the player's health bar completely, they will be sent to a snowy, wooded area. Soon after, wolves will appear from the distance and charge at them, damaging them and turning their vision redder and redder.
When this is over, the camera will cut to their bloody remains scattered in the snow.
|"Fur Oshus" (chase theme)|
|"Such strange prey you are."|
|"Let the cold consume you!"|
|"Death is near!"|
|"Why do you run?"|
- Unknown Specimen 4's quote "Why do you run?" and Specimen 8's quote "Why do you run, child?" are similar.
- They also both feature deer antlers despite Unknown Specimen 4 being based off a wolf and are both able to control animals.
- She is a reference to several Inuit folktales such as the Fox Woman.
- Also possibly similar to Navajo's mythology, Skin-walker.
- The reason for her non-frightening appearance is simply because Akuma Kira was tired of drawing creepy things, so they decided to make something cute.
- In the error messages, Unknown Specimen 4 is referred to as "Tiri".
- Unknown Specimen 4's theme "Fur Oshus" was created by Jarren Christ, who also made the End Credits theme and the Spooky Kart Minigame theme.
- Despite being canonically female, Unknown Specimen 4 has antlers, something which only male deer have. However, in the case of the reindeer, or caribou, antlers are present in both males and females.
Unknown Specimen 4 and the shadow animals now have fully 3D models and Unknown Specimen 4 posseses a light blue glow around her.
The shadow animals have animations for waving their tail and ears, and will sink into the ground after being struck with the axe.
Unknown Specimen 4 now has her own starting room, consisting of a snowy forest with cobble walls (similar to Room 551). A cabin stands in the middle between the entrance and exit of this room. As the player approaches the cabin, the screen will turn blue. If the player walks by the cabin, Unknown Specimen 4 will spawn at the entrance door of the room and the chase will begin.
A dim starry blue screen overlay replaces the light blue mist that was originally present.
The shadow animals are larger and take a single hit to kill. If cobwebs spawn next to one of the shadows, they can both be destroyed with a single weapon swing.
She will no longer float back when she attacks the player; she now deals 45 damage with a delay of 3 seconds. Unknown Specimen 4 also received a slight nerf in speed, now going at the same speed as Specimen 2.