The Spectre Staff is a weapon that occasionally drops from Ragged Casters. Projectiles fired from the Spectre Staff will proceed in a straight line. However, if there is a nearby enemy or if the projectile comes in range of an enemy, it will alter its trajectory to home in on that enemy. However, projectiles do not home towards other players in PvP.
Spectre Staves are banned on many servers for their ability to cause extreme lag. If the bolt doesn't find an enemy, it can cause a sudden lag spike affecting everyone.