Gateways to Hell may have been discovered in the depths of planet Mars, which would soon be rendered by surviving lone marines. But that might not be the only gateways to the dimension of ultimate evil and suffering.

Perhaps another gateway may be buried in the deep caverns in Equestria. Perhaps somepony decides to open it by accient, but then shut it down before anything could happen.

Or perhaps some pony knows of its existence and power, and is mad enough to open it to unleash an unspeakable evil.