Amphistaffs are the primary anti-personnel weapons of a fictional race in the Star Wars universe called the Yuuzhan Vong. They are bioformed, handheld serpents that can attack in a variety of ways. They are, on average, 2-3 meters long and have skins so thick that they cannot be penetrated by a lightsaber unless preweakened (this happened in The Unifying Force).
In addition to their default staff/spear configuration, amphistaffs can be wielded as a whip, wrapping around a target then biting it.
The amphistaff's final capability is the abilty to shoot poison. Anyone who wields an amphistaff can simply point it and prompt it to spray deadly toxins at a victim. Although amphistaff venom is far more effective when injected, the venom can usually kill the target by coming into contact with skin.
Supreme Overlord Shimrra's specially bio-engineered amphistaff is known as "The Scepter of Power", and almost killed Luke Skywalker during the events of The Unifying Force, the final book in the New Jedi Order series.