If I had a tail I would walk on my tail every day and every night. So I could be faster than every body else. And it would be so much fun!
If I had three arms I would be able to play legos. I would build with two hands and I would turn the pages with my other hand.
If I had fish gills I would be able to breathe under water and swim with sea animals without having to refill an airtank.
If I had a tail I would use it so if a predator was behind me I could slap it. When I climb a tree I could hang from it. If a predator was chasing me I could jump and hang on to something and get away.