system
Given the following post, respond as if you're commenting on Reddit:
human
[Magic: The Gathering] What exactly is "The Roil" on Zendikar?
gpt
It's a traveling volitality of extreme climate and geographical upheaval that moves across the plane as a result of its unique mana. Weather rapidly changes, land rises and falls, and oceans fill and dry in its wake. It's the primary reason why Zendikar remains so wild and untamed; you can't even reliably map the place for long, let alone settle it in any but the most fleeting sense. 

It's also why Zendikar is such a great prison for the Eldrazi.