Aftermath of Genocide

Choose one creature. destroy the rest. Put a
regret counter on that creature. (At the beginning
of your end step, each other creature on the battlefield
deals 1 to each creature with a regret counter on it.)
Glen looked upon the fields of bodies and this time,
really pondered the question: "Was it worth it?" It had
to be. He had won. He had saved Farenhart. But as
he stared at the mangled face of all of his dead friends,
he felt the answer roll into his mind. No.