Durgā is the goddess who gives durgaghna (the removal of difficulties, or removal of bad ways). Her prasiddha mantra has 7 words and 17 syllables.
||Oṁ Hrīṁ Śrīṁ Klīṁ Durgati-nāśinyai Mahāmāyāyai svāhā||
Oṁ triple formed Goddess, who is the Great Illusion, destroy my bad direction, so be it.
This mantra is very beneficial during Rāhu daśā and especially Rāhu antardaśās. Durgā is the general remedy for Rāhu. If Rāhu is conjunct the Moon, then Durgā becomes the primary remedy.
The Navākṣarī Stotra gives the famous Navārṇa mantra, which is 5 words and 9 syllables, placing the Devī in the lagna. This is the best mantra when Rāhu, or Moon afflicted by Rāhu, has a relationship to the dharma trines. When Oṁ is added to the front of the mantra, it becomes the Rāma Tāraṇa mantra, which is what Rāma used before going to battle against Rāvaṇa (a Rāhu-like demon). This mantra has 6 words and 10 syllables, associating it with the artha trines. The mantra is:
||Aiṁ Hrīṁ Klīṁ Cāmuṇḍāyai Vicce||
Oh Triple Goddess, Remover of the dual fluctuations of the mind, cut away ignorance.
asya śrīnavārṇava mantrasya | brahma viṣṇu maheśvarāḥ ṛṣayaḥ gāyatrī uṣṇik anuṣṭupchandāṃsi | mahākālī mahālakṣmī mahāsarasvatī devatā || nandāśākambarībhīmā śaktayaḥ || raktadantikā durgābhrāmaryo bījāni || agnivāyussūryastatvāni || home viniyogaḥ || agnau puṣpaṃ | āvāhana pādyādi || aiṃ hrīṃ klīṃ cāmuṇḍāyai vicce || 108 || Agnikāryapaddhati
When Rāhu is in a Mars sign, or aspected by Mars or Saturn, it takes a more cruel form (ugra), or we can say more intense energy is needed to give remedy. In this regard one should call Durgā as Cāmuṇḍā or Caṇḍī, and accordingly use those mantras. This is the prasiddha mantra of Caṇḍī:
Oṁ praises to the fierce Goddess [who can remove the negative].
The Achyutananda tradition teaches another distinction between the Navārṇa and Caṇḍī mantras. The Caṇḍī mantra is associated with Caṇḍa and the Navārṇa mantra with Muṇḍa. Caṇḍa and Muṇḍa are the two demons that the fierce form of Durgā destroys. Caṇḍa means angry, wrathful, cruel or violent, and represents pain and confusion in the heart. Muṇḍa means low, blunt (lack of sharpness), pointless (also hornless or shaved), and it represents pain and confusion in the head. If the lagna or lagneśa is afflicted by Rāhu, then the Navārṇa mantra is indicated. The navārṇa mantra gives lagna correction; it removes the traps and confusions of the brain. The Caṇḍī mantra relates to the fourth house and the removal of the traps, pains and confusions in the heart.
[These webpage is printed in Science of Light Volume 2, p.410]