Slayer staff, Staff of Light, Staff of darkness, or Abyssal wand
Click animation for full size
Slayer Dart (formerly Magic Dart) is an air spell that requires 50 Magic and 55 Slayer to cast. 55 Slayer is only required if you are using the slayer's staff. It may only be cast if a slayer's staff, a staff of light, a staff of darkness, or an abyssal wand and orb are equipped.
Slayer Dart is the only magical combat spell that can damage a turoth or kurask, along with the leaf-bladed sword and leaf-bladed spear being the only melee weapons and broad-tipped bolts and broad arrows being the only ranged methods that can damage them. The runes for Slayer Dart are also a reward from all Slayer Masters when you trade in points after completing the quest Smoking Kills.