Phasm

In the Dungeons & Dragons fantasy role-playing game, the phasm is an aberration. It resembles an amorphous blob of giant, brightly colored cells, organs, bacteria and ocean plants, roughly five feet in diameter and two feet tall, but can assume the form of almost any object or creature by developing a caste around these innards. (The creature may be a bizarre form of life which has developed its organs and microsomes but has yet to obtain a permanent outer form.) It lives in organic, underground caves.

The phasm, though classified as an aberration, has similar habits to an ooze when in normal form. When harassed or pursued, however, it morphs in the shape of and develops the form of the deadliest creature it knows, and then attacks in whatever way it can in that form. When in natural form, it can attack with a pseudopod. The phasm is highly valued for various medical reasons and for study.

Rather strangely, a phasm can speak. It speaks Common. It prefers to communicate telepathically, however.

They are chaotic neutral in alignment.

Powers and Abilities
The phasm is a shapechanger, able to assume the form of any corporeal creature. It can also communicate telepathically.