In doll form- which he often assumes when hiding from the gaze of 'those dashed blighters', Sir Nigel appears to be an ordinary children's doll; only the small glass bottle of blood in his chest and the eyes which reflect slightly more than the available light suggest he is anything special.
When interacting with anyone else however he usually makes use of a hat of disguise to assume a replica of his former self, only about half a foot in height; that is, a gentleman human in top hat and monocle and beautifully tailored black waistcoat and trousers about the same height as a small dagger. This peculiar sight is heightened when he rides his pet hawk (pheasant), a bird named Bertie, who hovers patiently while his rider converses pleasantly with people.
When in combat (in the thick of battle, my good fellow!) he illustrates all his spells with commanding pointings of the second digit, usually followed by a few barked arcane syllables bathed in an accent like extremely polite honey.