
She will be a living monster generator. I know I want her to be bipedal. I want her head to monstrous. I do not want her to look like Pathfinder's Lamashtu. She would be a BBEG. I would like to have a mate. She has gone by the name Echinda and she is also know as Hauathon.Is that ALL you know about her? What if she had all of the traits of all of the monsters in MM? She could be like some sort of living monster generator, like in Gauntlet.
I know that's a gross oversimplification, but without more of an idea as to what you want to do with her, it's hard to make any good suggestions.
What place is she going to occupy in the campaign? Is she the BBEG?
Sounds like an Aberration from the Far Realm.She will have the ability to create any monster she wants to.
The description below is the star of her true form. I would like the description to be more monstrous in appearance. I got the idea for the description from looking at the Mindwitness.
An Ancarotaur resembles a gigantic, extremely horrific looking starfish. Its smooth rubbery skin is oily and dark as the darkest night in color. Instead of the starfish arms, it has twelve symmetrically spaced incredibly flexible appendages. Two of its appendages are tentacles, measuring forty feet in length. Both of these tentacles have small but strong white sucker-like disks that are aligned in four rows. Each of its suckers is ringed with sharp teeth. These two tentacles are the most flexible of all its appendages. Four of the appendages split at the end, into three radial “fingers.” Another four of the appendages are nightmarish looking tentacles. A single vicious looking barbed claw is found at the end of these tentacles. Another two of its appendage are tentacles. At the end of these two tentacles is a vicious looking mouth. Each mouth is lined with a double row of eight inches long razor sharp pointed teeth. In its central disk, it has three round glaring red eyes that measure two feet in diameter set in an upside down triangle pattern. Above each of those eyes is a thick brow ridge. On both of each side of those eyes is a glaring red that measures six feet in diameter. All the eyes have a large rectangular shaped pupil. Below all of its eyes is a large powerful round mouth lined with sharp, serrated, triangular teeth. Instead of a normal tongue their mouth has five black tentacle-like tongues that when fully extended, are about a third the length of their body.
I have like the Deepspawn since I first saw them In 2nd edition D&D.The Deepspawn is a monster quite similar to what you want, although the outward appearance is drastically different (but that is just fluff, so change as you like). Deepspawn are very intelligent aberrations that can reproduce any corporeal creature they have previously eaten - including ALL abilities, be they derived from class, type, race, whatever, and also including funtional masterwork equipment. Yes, that's right, a Deepspawn can create a horde of Elminsters under its control once it gets to eat Elminster once. And all of those Elminsters would have Elminsters full memory, spellcasting prowess etc.
They first appeared in Monsters of Faerûn, but they're bound to have been reprinted at some point.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.