A variety of well-known artists make a special appearance on "Hydra" including Tarja Turunen (ex-vocalist of the symphonic metal band Nightwish), Xzibit, Howard Jones (ex-Killswitch Engage, Devil You Know), and Dave Pirner (Soul Asylum). "Hydra" comes in a variety of formats including a single disc version, a double-disc version with Within Temptation covering songs by Imagine Dragons, Lana Del Rey, Enrique Iglesias, and more, a limited edition vinyl box set that includes "Hydra" on double vinyl, and instrumental cd, media book, song book and guitar pick, and a stand alone double-vinyl piece.