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. They share no physical attributes with each other as other races do. All Eldrazi decend from one of the three Eldrazi Titans. The ones closests to the Titans in power are colorless and huge, while the lesser drones are aligned with different colors of mana and smaller than their brethren.
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.