The Monster Manual states that Dragon Turtles are “among the most fearsome creatures of the oceans. As large and voracious as the oldest of its land-based dragon kin, a dragon turtle strikes with its deadly jaws, steaming breath, and crushing tail.”
The Monster Manual describes jinni as “rare elemental creatures out of stories and legend. Only a few can be found on the Material Plane. The rest reside on the Elemental Planes, where they rule from lavish palaces.”
The Monster Manual describes Displacer Beasts as a “monstrous predator that takes its name from its ability to displace light so that it appears to be several feet away from its actual location. A displacer beast resembles a sleek great cat covered in blue-black fur. The beast’s eyes glow with an awful malevolence that persists even in death.”
The Monster Manual describes Kuo-toa as “fishlike humanoids that once inhabited the shores and islands of the surface world. Long ago humans and their ilk drove the kuo-toa underground, where they dwell in everlasting night. Kuo-toa can no longer abide daylight."