He could potentially do... something much worse. You already tried the "MAUL HIM" option, but that didn't work out for you very well. This isn't the most advantageous situation for trying to maul a magician wielding real magic. Besides, you have always wanted to be picked as the volunteer in magic shows. You didn't exactly volunteer this time, but it's close enough. You give in and help him.
You reach out to place your white paw on the magician's shoulder. You aren't quite used to standing as a bear yet, so you almost lose your balance before your paw reaches his shoulder. It's a little embarrassing. Seeing your furry paw, being incapable of speech, and barely being able to stand all rub in the fact that you aren't human anymore. His shoulder feels fragile under your puffy paw pads. You resist the temptation to dig your claws deep into his shoulder.
"Good boy. You made the right choice, bear," the magician says as he pats your protruding belly. You reply with a displeased snort.
"You don't get stage fright, do you, bear? I want you to be the main attraction. ...And you will get to work with my beautiful assistant!" He must have added that last part because he can sense you are still reluctant. You don't respond this time. You just continue looking down at him.
"Come. We have a lot to rehearse, my massive polar bear friend!" There's a poof and a cloud of smoke envelops both of you. When the smoke clears, you aren't in the basement anymore...