Unknown Specimen 4, referred to as Tirsiak in the game files, is one of the new specimens encountered in the Endless Mode.
Tirsiak is one of the most human-like specimens seen in the game. She has short white hair and amber-colored eyes. She also has the ears and tail of a wolf, which are the same color as her hair. She also has a pair of brown deer antlers which seem to be wood-like in texture. She wears a brown top with a shawl and skirt both made of dark brown fur. She also has brown arm warmers lined with cream colored fur and brown leggings with a band tied around the right knee. She is also barefoot. Lastly, she wears a necklace with various gold beads on it.
The rooms Tirsiak chases you through will be filled with bright blue mist, and the silhouettes of wild animals (moose, bear, wolves, etc.) will appear blocking the player's path. The player must destroy them with the axe in order to continue. She will do 1/4 or 1/5 damage to the player upon contact. Whenever Tirsiak 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 the player, damaging them and turning their vision redder and redder. When the player eventually dies, the camera will cut to the player's bloody remains scattered in the snow.
"TIRSIAK AMB", Unknown Specimen 4's chase theme.
Unknown Specimen 4's sounds when the player 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, make Tirsiak a far larger threat. She will no longer float back when she hits the player; this is replaced with an attack delay of a couple of seconds.