What does it mean if you dream you change into a black panther?

It Depends on the situation, if you see it as a threat or just passing by,

Panther

To see a panther in your dream, signifies lurking danger and enemies working to do you harm. It represents darkness, death, and rebirth. On a more positive note, panthers signify power, beauty and/or grace. Consider the feel of your dream to determine which meaning applies.