You're human mind is somewhat torn. Despite this thing that she's done to you, your mistress has been kind and offered you tasty food and warm gentle back rubs. Still it's really only so you'll give up on humanity and become her cat forever. Whoever this man it, he's clearly her enemy. Does that make him your friend?
Your cat-mind is completely unhelpful, preferring to stay hidden and safe. You finally make your decision. Your mistress has made you a promise and is much less an unknown then the Obi-Wannabe fighting her. Still, how best to help her. You glace around the room to see what it is that you can use to help with. You see that several books have been knocked off the shelves allowing much more room for a small body to fit upon.
Calling upon your instincts for stealth you take the long way around while the sorcerers concentrate on each other. You crouch down and leap up on a shelf directly behind the man in the grey cloak. You make your way across the shelf to a small bookend shaped like a dragon and use your back legs to push it over the edge. It hits the ground with a dull thud, a glass sphere held in the statuette's claw shattering as it hits the ground.
"Wha..?" the man says, briefly distracted by the noise. It's all the distraction your mistress needs. She pushes forward with a burst of energy, enveloping the man in the robes. Tendrils of energy wrap around his arms, pinning them to his sides, and his legs pulling them together. He falls backwards as he loses his footing.
"Hmm...so concerned with appearances." your mistress says with a sly grin. The mans starts to reply but his mouth slaps shut as his lips push out and harden, shifting to a yellow hue. The dyed hair on his head turning blue as a single feather stretches out atop his head. His face narrows as his beard becomes smooth and blue. His arms broaden and flatten as feathers replace his fingers and skin. He struggles to a standing position, but falls again as his neck narrows and lengthens as blue feathers crawl down it. His body becomes round and squat as his feet change, becoming bird-like appendages. He shrinks beneath his robes, but you can see the last stages of his change as a fan of colorful feathers sprout from beneath the robe. Within moments a bird struggles out of the robes that the man once wore.
"You're a pretty little peacock..." she says and takes his beak in her hands as she stares into his eyes "...aren't you." Something in the birds posture changes. He begins moving about as a regular bird would. She smirks and stands before shooing him out of the room, and presumably out of the house. She returns moments later to find you sitting on your haunches, looking at her through narrowed eyes.
"Hmmm...clever kitty. Using a perfect blend of human and cat. Perhaps it's time that your body reflected that." she says.