Jaya- Mahabharat

शिखण्डिनी - Shikhandini

Thereby Parashurama entered Hastinapura and challenged Bhishma to duel. Bhishma gently bowed, and said "Why Gurudev, why do you want to fight me?" 
From behind Parashurama emerged a fierce looking Amba. Bhishma's lips formed a mild smile, his eyes softening with compassion. "It is not I, who wronged you Amba. I don't see why you shall avenge me in this way"
Amba replied sternly, "You took away my life, Bhishma. Had you not barged into my Swayamwar and ruined my right to choice, I would have lived as a wonderful wife, and birthed righteous children. But you ruined all of it. You brought upon destruction and wrath yourself. Face it now."
Parashurana tightenes his grip. Bhishma sighed, "So be it then. Go forth, Gurudev" He said.
And as the skies became clouded by their arrows and weapons, a stretched duel began. Parashurama, was an Avatar, and he couldn't be killed. Bhishma had boon from his father, and couldn't be killed. And both did not want to kill each other, both deeply respected each other. They both wanted to merely defeat the other, and as time passed, both realized that it won't be possible for them to defeat the other without killing them, because these valiant warmen would not give up until slain dead.
But both couldn't be killed. One was a divine incarnation, and the other had the boon to not die until choosing to die. Thus their battle continued for days and months and years. When thus their battle knew no ends, Parashurama began to get anxious, and shot powerful missiles. Bhishma had to retaliate by equally destructible weapons. The effect of these weapons began to torment the life around. The Devtas became concerned.
And thus, when their battle was becoming harmful, yet stood unending, one compassionste Rishi, Devarshi (the rishi of Devtas) Sri Narada came down. Narada, the wise, intellectual and devoted Rishi, approached Parashurama and said "Narayana Narayana (several side texts mention Narada to be cursed (or blessed) to always chant Lord Narayana's name)".... "Bhagavan Parashurama, what are you doing? You who saved the world from torment of anarchs and monarchs, you who crossed boundaries of being Brahmins in purview of welfare of world, and took to arms, why are you now engaging in this war, which is endangering world? Why do you fight this Bhishma, who although seemingly has caused trouble to Amba, had no intent of doing so, and who was thinking in welfare of country and people? Please be pacified and back off, O Lord"
Hearing Narada's kind and intelligent words, Parashurama agreed. He blessed Bhishma to be considered victorious in this battle, and he cast one final merciful glance upon Amba, "Go and find solution from gods, Amba" and he left.
Left alone, again, in the battlefield, Amba couldn't still give up her pain she was causing to herself. Her thirst for vengeance only grew, and she went to Himalays near the river Bahu, and performed a Tapas of Lord Kartikeya (the leader of the armies of Devtas, and the son of Lord Shiva).
When Kartikeya was pleased, and knew of the episode, he gave a garland to Amba and said, "whichever king wears this garland and fights Bhishma, shall win" and he disappeared.
Amba, happy, again went to all kings, but to her astonishment, none agreed. How could any king believe this lady again, when they were all already defeated by Bhishma, and when Bhishma had defeated Lord Parashurama himself! There was no point in dreaming of defeating Bhishma. It was better to remain friendly with him.
Enraged, Amba threw the garland high up on the air, when she came out of the palace of Raja Drupad of Panchala. The garland landed upon an archway of the palace entrance. Amba went to the Himalayas, and on banks of Gangotri, she performed the fiercest Tapas, by standing upon only one toe, the other leg folded to balance on the standing leg's thigh, and hands in folded position, pointing high towards sky, her mind fixated on Lord Shiva.
After several years, Lord Shiva appeared. And he neednt be explained again about the whole deal. But Amba, knowing that she camnot trust anyone anymore, decided to avenge Bhishma herself, and said, "I desire to kill Bhishma"
[This is the point where Amba really made a mistake. When the lord of worlds, Lord Shiva appears, she could've asked for anything, good and positive. Instead she still denies to forgive wrongs occured to her in a bit of confusion, and continues to seek vengeance, and invokes Lord Shiva himself, for her revenge]
Lord Shiva, compassionate, says "That shan't occur in your this birth, Amba. In your next birth, it certainly will be"
And he disappears. Amba, eager to seek vengeance, immediately decides to end her life. She lits a huge pyre, and burns herself to death, ending her life.
She is thereby born as the daughter of Maharaja Drupad of Panchala, and she is named Shikhandini.