Flamelash

Flamelash is one of several Magic Weapons found throughout Terraria, obtained as a rare drop from Bone Serpents. When cast, it launches a mouse-controllable ball of fire, which also emits a small light radius, and gives off embers which fall through the ground. As it costs only marginally more Mana to cast, but inflicts more damage, it is considered a higher-tier version of Magic Missile. It can hit weaker monsters twice, such as slimes, without causing the fireball to dissipate. (Stronger monsters need confirmation)

http://www.youtube.com/watch?v=5RX0iJLVO84 - Video guide

Tips and Strategy

 * Because it emits numerous amounts of light particles, it can be used as a "surface scanner" because the particles fall deep within the ground, helping find valuable ore in the ground that otherwise would remain unseen.
 * Because of its controllable nature, this weapon can be effectively used to safely clear out overgrown dungeons.