During the Worldwake, many traditions and customs were disrupted by the volatile land. An assault by land-elementals interrupted a ceremony called the Ritual of Lights. The attack wounded and killed a number of the humanoid ritualists, ending the chants and scattering the sacred candles. The result is the awakening of an ancient being made of pure mana - Omnath, the Heart of Zendikar's Mana
Deep in wilds of the continent of Ondu, on top of a vast mesa, through a dense thicket of dangerous woodland, in the center of a murky marsh, inside a binding circle of seventy-seven candles, trapped in the invisible depths of an unfathomable pit, lies the Prison of a being known as Omnath. The stories tell of Omnath as a being made of pure mana, a manifestation of Zendikar's chaotic, primeval forces that would wreak massive destruction if it were released. Although skeptics wonder whether anything actually lurks there and whether such a thing is even possible, the devoted pilgrims who travel there claim that only their faithful recitation of the Ritual of Lights has contained Omnath and its terrible power.
But Zendikar is changing. The old bonds that have kept Zendikar dormant have been broken. The candles have been snuffed. The Prison of Omnath has been destroyed, and Omnath is loose again.
It gathers against the coming storm.