Traits

Your Perfpal's legs can be replaced with a mermaid's tail. The tail must be a realistic length. 
The tail must be that of a fish, not another aquatic life form.
(Aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits)

(This allows for an alternate "form" if you'd like for your Perfpal to have access to legs still.)

Gills can be placed on any plush part of the body. They are purely cosmetic and have nothing to do with a Perfpal's breathing.

Permanent seaweed growth is possible on any part of the body. Seaweed can be any color and any length. 

Can be added in any amount on any part of your Perfpal, excluding on the hooves directly. The fins can come from any marine animal that has fins. They must be a realistic length.

Waterbed stuffing allows for your Perfpal to be filled with water instead of having regular stuffing. This causes the Perfpal to move a bit differently. The water can be any color. (Named after the furniture term and not the ecology term)