The Protuberance is an elemental grenade launcher. It fires an explosive round in an arc, which MIRVs into three more explosions upon impact. This makes it excellent for crowd control and dealing huge amounts of elemental damage. Care must be taken as the splash damage can easily kill the character if used at close range.
The gun is especially useful for an elemental focused Amara, guaranteeing the damage over time effect and increasing damage overall.