Unknown Specimen 4, referred to as Tirsiak in the game files, is one of the specimens encountered in the Endless Mode.
Tirsiak is one of the most human-like specimens seen 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. Tirsiak is also barefoot.
Tirsiak'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 protagonist's path. The animals must be destroyed with the axe in order to get past them. Tirsiak will do 1/4 or 1/5 damage upon contact. She goes through walls and obstacles, and is unaffected by the axe. Whenever Tirsiak damages the protagonist, she will float backwards.
If she depletes the protagonist'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 the protagonist eventually dies, the camera will cut to their bloody remains scattered in the snow.
"Tirsiak ambience", Unknown Specimen 4's chase theme.
Unknown Specimen 4's sounds when the protagonist is near.
"Such strange prey you are."
"Let the cold consume you!"
"Death is near!"
"Why do you run?"
- Tirsiak'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 Tirsiak being based off a wolf and are both able to control animals.
- She is a reference to several Eskimo/Inuit folktales such as the Fox Woman.
- The reason for her non-frightening appearance is simply because Akuma Kira was tired of drawing creepy things, so he decided to make something cute.
- In the error messages, Tirsiak is referred to as "Tiri".
Tirsiak now has a full 3D model.
The shadow animals appear to be larger, and take more hits to kill. This, combined with the new mechanics of the weapons, makes Tirsiak a far larger threat. A starry blue screen overlay replaces the blue mist that was originally present. She will no longer float back when she attacks the protagonist; this is replaced with an attack delay of a couple of seconds. Additionally, as with the axe in the original game's Endless Mode, using the sword has no effect on her.