Demonic merfolk swim the abyss of astral waters. They have genetics of a demon often ubi parent and a mermaid/man. For this reason it is common to see some of them with more demonic features such as horns, different colored hair and skin along with other natural designs that their aquatic ancestors would not possess. These entities tend to be sexual or territorial depending on the individual. All who I have encountered have been very dark arts. They're not afraid of causing some mischief and bringing you on a dark path if interested. If you have a lot of water-based entities in your keep like light natured mermaids/men I suggest getting one that is mellow in personality. Their abilities include but are not limited to things like energy manipulation, water magick, black magick, absorbing energy from other sources and giving it to you, aid in remote viewing, bonding with oceanic immortals and aura cleansing.