During the fight with Percy Jackson, Thalia Grace, and Nico di Angelo, he was shown to be able to almost kill them with his spear. He is very fast with it too, seeing as how he stabbed a rock where Percy had been standing a half- second ago. He kept Thalia busy, fighting her while she had two Hunting Knives.
When Bob appears in Tartarus, his spear now has the form of a broom, but he is able to extend the spear out of it. Percy notes how handy it is as it can act as a boomerang as well and Bob can call it back to his hand. It is destroyed by Tartarus and is apparently connected to Bob as its destruction hurts him badly.