I can't think of a good story here, so let's just get to it.
You somehow have all the powers of a god now. And you have been forced by something to use that power to destroy all life on earth. You can say "volcano" and a single volcano will find a way to destroy earth. Or you could say something detailed like "horrible virus that turns everyone into werewolfs, and then terrorists use nukes to..."
And no matter what you say, it will cause the end of the world.
You somehow have all the powers of a god now. And you have been forced by something to use that power to destroy all life on earth. You can say "volcano" and a single volcano will find a way to destroy earth. Or you could say something detailed like "horrible virus that turns everyone into werewolfs, and then terrorists use nukes to..."
And no matter what you say, it will cause the end of the world.