He holds a vajra (thunderbolt) in his right hand, which emphasizes the power to cut through the darkness of delusion. Vajrapani looks wrathful, but as a representation of the enlightened mind, he’s completely free from hatred.
Vajrapani’s mantra is simply his name, which means “wielder of the thunderbolt”, framed between the mystical syllables Om and Hūm. This mantra helps us to gain access to the irrepressible energy that Vajrapani symbolizes. A familiarity with Vajrapani does, of course, help here, although the sound of the mantra is itself rather energetic.