Dwelling within lakes, rivers, streams, seas, and oceans, Aquan encompasses any monster adapted for aquatic locomotion. Primarily amphibious, although certain species may simply be semi-aquatic, the Aquan phylum is distinguished by a streamlined body, webbed appendages, possession of gills or porous skin, and an enlarged lung capacity.

The main defense of the Aquan phylum is their ability to release concentrated streams of highly pressurized water from a storage sac located in their abdominal region. Glands near the sac produce salt and dust of magnesium and iron, formed through ingestion of these substances as a part of their omnivorous diet. The mixture boils the water in the storage sac and muscle contractions force the water up through the vestibular tube and out through the mouth at high enough pressure to cut through solid steel.