Eldrazi
The Eldrazi are an ancient race native to Blind Eternities that have "transcended colors of mana altogether". Their hunger for energy is a threat to every plane they enter, as they feed on the planar mana until its death.
Zendikar
Millennia ago, three Eldrazi entered Zendikar. They were sealed away by three Planeswalkers: Ugin, Sorin Markov and unnamed lithomancer. Now, someone or something has weakened their prisons. Sorin Markov, has returned to Zendikar in the hopes of resealing them. Nissa Revane, a young elf planeswalker who lives on Zendikar, aims to have them removed from Zendikar altogether, as she considers them far too dangerous to keep around.