A disc of debris swirls around the sun for hundreds of thousands of years before slowly coalescing into a new planet. As the planet cools, oceans form and clouds fill the atmosphere. Organic molecules begin forming into more and more complex structures until they become what we would now call a wolf, a bear, and a lamb.
The alien's eyes begin burning with the fury of a thousands stars at the sight of these twice-evolved mammals. "I am your reckoning!" he bellowed and swung his mighty sword over his head.
