Mahish, the king of the demons and usurper of the throne of heaven, was shocked and enraged by the disastrous events on the battlefield. He reverted to his own form, a buffalo, and charged about on the battlefield. He ran wildly at Durga's divine soldiers goring many, biting others and all the while thrashing with his long, whip-like tail. Durga's lion, angered by the presence of the demon-buffalo, attacked him. While he was thus engaged, Durga threw her noose around his neck. To escape this trap, Mahishasura discarded the buffalo and assumed the form of a lion. Durga beheaded the lion, and the demon escaped in the form of a man. Without hesitation, Durga dispatched the man with a flight of sharp arrows. Yet again the demon escaped, and this time took the formidable shape of a huge elephant, which battered Durga's lion with a tusk. With her sword Durga hacked at the tusk until it too was broken. 

Weakened, the demon reverted once more to his own form the wild buffalo. He retreated into the mountains where he hurled boulders at Durga with his horns. The Mother of the Universe drank the divine nectar, gift of Kuvera. She jumped on Mahishasura pushing him to the ground with her left 
leg. She grasped his head in one hand, pierced him with her sharp spear held in another, and with yet another of her ten hands she wielded her bright sword, beheading him. At last he felldead, and the scattered surviving remnants of his once invincible army fled in terror. 

The gods returned to heaven, and along with the sages of the earth, they sang praises to theGoddess Durga. Henceforth, and to this day, the Goddess Durga is worshipped by all the gods in heaven, and all human beings on earth. As he requested, Mahishasura is there too--frozen in his moment of final defeat, impaled by Durga's spear and prostrate beneath her left foot.source: www.parallel.park.org/India/Durga)