Monsters
Though many strange and fantastical beings in the mortal mind have been called by this name, "Monster" also refers to the beings of Milosian mythology that dwelt in the Underrealm before being drowned by their children, the Hadrash. They were said to be unfathomably gigantic, with minds either too small or too great for mortals to comprehend, and their vicious cruelty extended far beyond our understanding. They came in countless shapes and forms, and though some of their temperaments might have varied, they were uniformly evil and incapable even of cooperation with one another.
Though they were covered by the Seas of the mortal world, the Monsters were immortal, so Milosian myth is replete with tails of such beings coming up from the depths to terrorize mortal kind. Of course, there were similar tales of the Hadrash doing the like. The main difference between these two kinds of creature seems to be size, as well as the Hadrashi ability to cooperate and therefore form bands or even armies to fight against mortals.