Once upon a time, when the God Purphoros raised arms against Heliod, he crafted the Sword of Chaos which was capable of damaging the substance of Nyx. When Heliod and Purphoros clashed, it damaged the celestial resting place of Polukranos, World Eater and the hydra fell to Theros where it was sealed by Nylea and Heliod under Nessian forest.
At the moment of the clash, Elspeth just had planeswalked to Theros for the first time. She saw the Sword of Chaos falling from the sky, grasped it and planeswalked away. When she returned to Theros, ten years later, Heliod was angry at her at first. But when the God realised she might be the Champion of the Sun reborn he reforged the sword into the Godsend. Elspeth used her new weapon to defeat the awakened Polukranos.
Journeying into Nyx, Elspeth also defeated Xenagos, stabbing him with Godsend. But as a "reward", Heliod told her that no champion should know more than her god and because she knows and had seen places he didn't know, he stabbed her with the sword-spear, which shattered afterwards. Dying, Elspeth became confined to the Underworld of Erebos. A deathmask was forged for her, using the two jewels of Godsend.