The Change is able to do things involving change, hence it's name. In the anime, Change is able to swap the minds (or bodies) of two people. This swapping can only occur once a day, and if a change is not reverted after some time, it becomes permanent. Syaoran and Kero become victims of Change's ability in Episode 32. This resulted in a rather unique day at school and at home, before Sakura is able to reverse the switch a day later.
The Change appears as a blue chameleon-like creature. It shoots out its tongue to switch two people around.