post #1956272 post #2844658 post #3905417
Tem is short for Temmie. Tem(s) are small dog creatures found in Undertale at Waterfall. They can be found by taking a downward turn after the lowermost set of mushrooms is lit in the room with the mushrooms lighting paths (directly before the room in waterfall with the dimming crystal lights). The entrance is then at the bottom right. This pathway is hinted by the River Person, Undyne, and a sign near the save point by Napstablook's house, as well as a mention from Gerson, although he cannot remember where it is. (There is a debate if the tag should be Tem or Temmie due to no evidence which is correct. If tag is changed to Temmie, please edit wiki.)

See:

Temmie_(Undertale)