Selina has waist-length thick dirty geenish/olive blonde hair, fair skin, light brown eyes and purple lips. Her favorite color may be navy, as she wears a navy top with wavy black ends and a mesh collar with a pink circle. She also wears a navy jacket with high-collars and sleeves that end with spiked grey areas. Her stomach is covered with mesh, and she has navy gloves on her hands. Selina also wears a navy skirt with a chain-belt, which she usually uses to hang the shrunk Legendarium and navy high heel boots with gray tights.
Selina is intelligent and confident. She is not afraid of standing up to use her powers and of the Legendarium to others. She showed great respect and admiration towards the Trix and was willing to help them to take over the Magic Dimension's colleges in exchange for them to teach her the dark arts. But when the Trix refuse to share the power with her, she is shown to be a traitor, preparing schemes for her bigger goals. She is very loyal towards Acheron. She is shown to be very proud and protective towards the Legendarium, willing to defend it at all costs if needed. However, in the flashback in "Attack of the Sphinx", it is shown that she was timid and shy as she was unable to talk to a boy she appeared to have a crush on until Bloom made her.
After being redeemed and locking the Legendarium for good, she is shown to be kind, repentant, caring, friendly, loyal, brave and compassionate. She is also a whole lot more gentle, patient and calm than she was before.
As a fairy, the basis of her powers were never revealed. However, as a witch Acheron clearly states and dubs her the Witch of Snakes. As such, she could generate ethereal snakes and control them to her whims. Her ethereal snakes were powerful enough to destroy the Dragon Skeleton where the Trix held the magic schools' powers.She is shown to be the only one (except Eldora) who can bring legendary creatures to life, proof that the Trix uses her rather than stealing the Legendarium from her.
She is shown to be powerful enough to trap and hurt Bloom for a short period of time, and even then Bloom had to use a lot of power to simply throw her across a room without inflicting any other visible injuries.