The Nightmare Knives are a rare drop from the boss Nightmare. They are a Melee weapon and when used they are shot out at your enemy. They will go up to 5 feet ahead of you and then will come back. Each hit drains the enemies mana. The Nightmare Knives are very powerful against any Mage class enemies.
When fighting a Mage class enemy use these to drain their mana an render them useless.