Osushi

As a housepet, Osushi looks like nothing more than a fluffy white Pomeranian, his muzzle, ears, and paws tinted brown. That harmless shape hides his real nature. When he takes on his Dark Dragon form he swells into a towering black beast with a pale underside, four heavy limbs, a pair of enormous wings, dense scales, and a mouth crowded with sharp teeth.

In his canine guise Osushi is docile and obliging, happy to be used as bait or foisted onto strangers whenever Balgo needs him out of the way. The transformed Dark Dragon is another creature entirely, savage enough to try devouring the very people he lives with. Two months of soaking up Balgo's cruder impulses left him able to blurt out demands to see Noel's underwear, though he plainly has no idea what the words mean. By Noel's account he flares into his winged state whenever Balgo mocks him, sneezes, laughs too loudly, or lands in danger, and a bit of holding and petting is usually enough to shrink him back down.

The animal Balgo eventually named Osushi had actually met its end on London's streets, only for a Disguiser Dragon to slip into the corpse and reanimate it. Roughly two months before his true nature came to light, Balgo stumbled onto the little dog and took it home, never suspecting he was raising a Dragon. His secret broke open the day Balgo carried him to the spot where Noel had vanished, where he ballooned into the Dark Dragon and had to be talked down. He later relocated with Balgo to Reverse London, where his abrupt partial transformations, and his habit of parroting Balgo's rude demands, keep Noel and Ninny Spangcole endlessly busy.