Amphibiyte

Amphibiytes are hostile mobs that spawn in the Ocean Biome of the Overworld within Amphibiyte Caves. They are melee mobs that attack the player. They can also survive on both land and in water. Amphibiytes can swim quickly in water. The Amphibiyte is a hunter mob that can only be damaged if the player is at level 30 or higher.

'''Warning: Amphibiytes have a 1 in 50 (2%) chance of spawning Corallus upon death. Corallus is very difficult boss and thus players should take extreme caution when fighting Amphibiytes. Corallus has a pulling effect which makes it difficult to run. Do not take these on unless you feel confident that you can destroy Corallus. Visit Corallus's page for more information.'''

Trivia

 * The name Amphibiyte is derived from amphibians, animals that survive on both water and land.

References/Sources
http://adventofascension.gamepedia.com/Amphibiyte