Nightmare Vine

Nightmare Vine is an Herb that can be gathered by Herbalists.

Source
Nightmare Vine can be found throughout Shadowmoon Valley as well as Forge Camp: Wrath and Forge Camp: Terror in Blade's Edge Mountains and Throne of Kil'jaeden in Hellfire Peninsula. Prior to patch 2.4, it was only available in Shadowmoon Valley. It does not appear to grow any place in particular, it can be seen out in the open as well as tucked in between rocks. Requires 365 Herbalism to gather.

Nightmare Vine as an Ingredient
Nightmare Vine is used in the following recipes:

Alchemy

 * Destruction Potion
 * Elixir of Major Shadow Power
 * Fel Mana Potion
 * Fel Regeneration Potion
 * Fel Strength Elixir
 * Flask of Pure Death
 * Major Dreamless Sleep Potion

Enchanting

 * Superior Wizard Oil