Her appearance is similar to that of Omega Flowey in the original UT. After absorbing the human SOULS, Temmie transforms into a grotesque cat-like hybrid of cat parts, and machinery.
She has sideways jaws with two small, sharp teeth on each end as well as a small nose. The face also has two small eyes as well as ears and grey hair. On top of it, is a flatscreen TV. She also has metal pipes that connect to the face only. These metals pipes store the SOULS of the humans. She also has two large tentacles going across, connecting to her paws. Her paws seem to have small claws on them. Her fur seems to be white.
After defeating Toriel, Temmie appears to finish her even if you decide to spare her. She then absorbs the six SOULS and say that "in this world...it's kill or be killed." As she absorbs them, her face becomes horribly twisted and the game closes. When opening the game, it will appear different and the save file will be Temmies creation with the location being "My World" and the game being called "TemmieTale, or UnderTem". All of the players stats in UnderTem(?) are max level. Later, the player will find a save point that actually erases their save. Then the save point will get crushed and cracks. Then, a large Temmie face appears and "thanks" the protagonist for helping destroy Toriel's SOUL.
Later, the protagonist battles Photoshop Temmie