If you played both ARK and ATLAS, you'll know mermaids/sirens were in ATLAS but also modded back into ARK.

Name: Rahab
Age: 200+
Species: anthro Gigantopithecus cyclops
Bio: One of the many "monsters" engineered by Sir Edmund Rockwell, in order to establish a new primate for naval warfare against survivors came the Gigantopithecus cyclops or simply known as a "mermaid" or "siren" to sailing survivors. Rahab eventually broke free from Rockwell's control and began his own campaign to conquer the sea from opposing rivals.