Much is unknown of this enigmatic being. It is assumed that it is a Great Old One, or perhaps something else entirely. The being's name was revealed when Clark Ashton Smith, whom was a close associate to H.P. Lovecraft himself, received a letter from an unknown individual stating: "Yoth-Tlaggon at the Crimson Spring. Hour of the Amorphous Reflection... " 

Its appearance is nearly indescribable, but it appears to be a slug covered with scales and endowed with innumerable eyes. It also possesses a mask with the form of an inverted triangle.

The mask itself, however, is said to be the symbol of the cult of Yoth-Tlaggon which simply appears as an inverted triangle. This mask is a cursed object of great power that, according to the accounts of a Japanese writer, eventually fell into the hands of the Nazis, and they used it in some of their abhorrent experiments.