Even though She is from the Void and hence formless, Sri Maha Pratyangira Devi assumes a form so that we can comprehend who She is and what She is about. She is an epitome of the balance and Oneness between opposing forces, fiercely protects Dharma, and devours negative karmas. Her form reflects all these aspects.

Saints who have seen the Mother's energetic expression have described it as half-lion and half-human. The head is that of a male lion symbolizing courage, and the body is that of a woman symbolizing compassion. Her form and energy represent the balance between the masculine and the feminine, the union of Shiva and Shakti. It is a representation of yin-yang, the balance between opposing forces, enabling Her devotees to transcend dualities into Ekatvam, or Oneness with their higher Self.
The Mother is smiling, always in ananda, in great bliss, with laughter that of Ksham (pure bliss). She takes the ugliness of what we are holding, our karmas, She takes it into Herself and still presents Herself beautifully to us.
In Her full form, She is humongous, with 1008 heads (symbolically representing the 1008-petalled Sahasrara Chakra, the universal chakra of the cosmic energy) and 2016 hands, each hand carrying a weapon or sword for removing obstacles, or a symbolic item representing the attributes of a perfected Soul.

amma adi sakthi, swami shanmuga | adiyargal
Mother doesn't have a scary face
People say this Mother has a scary face. I tell them you have a scary heart.
Pratyangira Devi is riding majestically on a chariot pulled by four lions, representing the four Vedas (Rigveda, Yajurveda, Samaveda, and Atharvaveda) the four Yugas (Satya, Treta, Dwapara, and Kali Yuga), the four objectives of human birth (Dharma, Artha, Kama, Moksha), and the four stages of spiritual evolution (Sariyai, Kriyai, Yogam, and Gnanam). The jaws of so many lions make it very powerful for destroying negative karmas, and a great blessing for anyone on a spiritual path. She takes this fierce form to keep Adharma (unrighteousness) under check and to restore Dharma (righteousness).
In the current times, Amma Adi Sakthi and Swami Shanmuga had an open-eye darshan of Sri Maha Pratyangira Devi.