Cybermouse

From Tardis Wiki, the free Doctor Who reference

The Cybermice were a group of mice that Cybermen converted when they had settled down and tried to run a pet shop called Paws 'N' Claws.

After the Tenth Doctor and Rose Tyler defeated the Cybermen, they considered stopping the Cybermice. However when they did they found a mouse that resembled the Doctor already fighting them off. Ultimately they decided to leave, stating that K9 was the only pet they needed in the TARDIS. (COMIC: Untitled)