Asta settled as a ginger cat.
Before Malcolm reached puberty, Asta had not yet settled on a form, although she seemed to favour birds. She changed form often and with ease, usually for practical reasons. She also became adept at controlling her form, so as not to give away her's and Malcolm's emotions.
- "She had subdued her natural wish to change into something that could bite and threaten, and remained a robin." - Asta concleals her emotions.
Asta demonstrated the rarely mentioned ability to take the form of non-existant animals, by combining elements of different animals. She became an owl with a duck's feathers, to protect her from the rain. It is said that she only did this when no one but Malcolm was looking.
Forms taken included: Goldfinch, Kingfisher, Fly, Mouse, Squirrel, Owl, Swallow, Ferret, Robin, Moth, Monkey, Ladybird, Cat, Jackdaw, Greyhound, Hawk, Greenfinch, Kitten, Lemur, Butterfly, Crow, Rat, Badger, Butterfly, Snake, Terrier, Puppy, Leopard.
Asta was similar in personality to Malcolm, although often more observant than him.
- "When the lovers had passed she flew up to his shoulder and whispered, 'The man just along there - watch...' Malcolm hadn't seen him." - Asta notices something that Malcolm doesn't.
Asta and Pantalaimon developed a close relationship, as their counterparts Malcolm and Lyra did, with Asta watching over Pantalaimon, amusing him and consoling him.
Asta was horrified by Gerard Bonneville's malevolent hyena-dæmon, as Malcolm was, until Malcolm finally killed Bonneville and his dæmon.
- "Malcolm and Asta were terrified. She turned into a cat and burrowed into his arms, and he hid his face in her fur. They had never imagined anything so vile." - Malcolm and Asta watch Bonneville beating his dæmon