There’s a video of a double-headed cat-fish going viral on social media. The tape is said to be captured in Indonesia.
The situation of an animal having double heads is called Polycephaly.
Polycephaly is the condition of having more than one head. The term is derived from the Greek stems poly meaning “many” and kephalē meaning “head”. A polycephalic organism may be thought of as one being with a supernumerary body part, or as two or more beings with a shared body.