Enter Survival Mode. With your first shot, kill an enemy thing. If your first shot doesn't kill it, quit and start all over again. Wherever the bullet impacted the creature, stand on that. It'll be somewhere in the middle of the blood/corpse. Wait until creatures take you below 1/5 of your health, without moving. Without moving, kill all the creatures that were attacking you. If successful, you will receive the Blade Gun immediatley.