Roil
From MTG Salvation Wiki
The Roil is a phenomenon resulting from Zendikar's unique brand of mana. It causes extreme weather and natural catastrophes such as earthquakes and floods. The Roil changes the land and is the reason why the plane remains untamed and deadly.
For those born on Zendikar, the Roil is a natural phenomenon—just the way things are. To planeswalkers, it's obvious that this volatility is what keeps Zendikar dangerous, untamed, and without well-developed civilizations.
[edit] In-Game References
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