Deep one

The deep one is a new monster introduced in SLASH'EM.It's the weakest of the trio including it, the deeper one, and the deepest one,

Mythology
The deep one and it's related kin all come from "The Shadow over Innsmouth" by H.P. Lovecraft, creator of the Cthulhu mythos.

Encyclopedia Entry
For eighty thousand years Pth'thya-l'yi had lived in Y'ha-nthlei, and thither she had gone back after Obed Marsh was dead. Y'ha-nthlei was not destroyed when the upper-earth men shot death into the sea. It was hurt, but not destroyed. The Deep Ones could never be destroyed, even though the palaeogean magic of the forgotten Old Ones might sometimes check them. For the present they would rest; but some day, if they remembered, they would rise again for the tribute Great Cthulhu craved. [ The Shadow Over Innsmouth, by H.P. Lovecraft ]