Polukranos, World Eater

An ancient and unfathomably powerful hydra, though its modern-day status is as a living nightmare, the beast is known as Polukranos actually has its origins in the celestial realm of Nyx. Once content to slumber in its heavenly realm, Polukranos was cast down to the mortal realm in a struggle between the gods Purhphors and Heliod. There it rampaged, causing destruction and death unlike any seen since the Archon War.   Only once Heliod and Purphoros' battle was ended did the gods take notice of what their wrath caused. As Polukranos was a creature born of Nyx, the gods could not slay the hydra themselves and were instead forced to seal it away, trapping it deep beneath the lands of the Nessian Wilds.   The Tale of Elspeth Though Pulkranos had been successfully trapped, it would not remain there for long. Only a few short years passed before Polukranios managed to find its way out of its mortal prison, escaping to once again wreak havoc upon the mortal realm. Now filled an even greater hatred than before, dozens of mortal champions and heroes tried and failed to stop the hydra, each in turn losing their lives to its snapping jaws and pounding feet.   When the planeswalker Elspeth TIrel found herself on Theros, she chose to journey across its world to understand the gods. Eventually, she caught the attention of Heliod himself, who elected Elspeth as his new champion. The planeswalker's first task would be to take her spear, a weapon created by Purphoros himself and capable of destroying the star-stuff of Nyx and slay Polukranos.   World Eater's Death Though the journey to find Polukranos was arduous, and the battle between Elspeth and the beast was terrible, eventually, the hydra was felled, with the assistance of Elspeth's friend and lover Daxos. But as with all creatures that die in the mortal realm of Theros, Polukranos's spirit was carted away to the Underworld, to be trapped once more. There the monster's anger sits and boils, and though the Underworld is home to the most powerful jailors in Theros, so far no prison has been enough to hold Polukranos for long.