If she thinks someone is a threat, she bares her teeth, snarls, and looks ferocious. To someone on the wrong end of that snarl, she looks like a demon dog from heck. To someone she is protecting, the dog is like a guardian angel. In the Dharani Chapter, Kishimojin and her Ten Rasetsunyo daughters fiercely utter, "If there are those who fail to heed our spells and trouble and disrupt the preachers of the Dharma, their heads will split into seven pieces like the branches of the arjaka [basil shrub]."
"And at that moment Vajrapani the Yaksha, holding up a huge iron club, flaming, ablaze and glowing, up in the sky just above Ambattha was thinking, "If this young man does not answer a proper question put to him by the Blessed Lord by the third time of asking, I'll split his head into seven pieces!" The Lord saw Vajrapani, and so did Ambattha. And at the sight, Ambattha was terrified and unnerved, his hairs stood on end, and he sought protection, shelter, and safety from the Lord. Crouching down close to the Lord, he said, "What did the Reverend Gotama say? May the Reverend Gotama repeat what he said!"
Note that there is a whole Chapter of the Lotus Sutra devoted to the transformations of Kanzeon. He or she appears in various forms to meet the needs of those who summon up the heart of real karuna-compassion. The Kanzeon Chapter examples of people who find themselves in dire straits; they are attacked on the road by bandits, shackled in chains, about to be executed, victimized by spells, and so on. In each case, if the person calls on Kwan Yin, they are saved. The bandits freeze in their tracks and become kind hearted. The chains are loosed. The executioner's sword shatters into seven pieces. The curses are returned to the sender. My take is that is these examples dramatize or illustrate the incredible redeeming, conciliatory, and healing power of Maha Karuna 大悲 {daihi; dabei} or Great Compassion. I suspect that the idea is, when we confront enmity, malevolence, or cruelty; whether in ourselves or others, to channel Kwan Yin (who represents the merit of Great Compassion) within our heart 心.
Like Kishimojin, Tara plays a protective role, and has both fierce or wrathful and mild or benevolent forms. There are many legends about Tara's origin. According to one, she started out in Hinduism as a blood sucking demon; but something happened to arouse her heart of female protective compassion. After that she become a benevolent goddess. This parallels Hariti's {Kishimojin} transformation from a Raksha demon; who fed human children to her own Rakshasha children, to a benevolent angelic being that protects children of all species. "Green Tara, who embodies active female wisdom, is sometimes called the 'Mother of All Buddhas'. She manifests in many emanations; both peaceful and wrathful in form. The merits acquired from the Green Tara meditation are quick thinking, practical wisdom, skillful compassion, generosity, magical powers, fearlessness, spontaneity, and general protective-ness." ~~ Green Tara Mantra