Hydra is the sixth studio album by the Dutch symphonic metal band Within Temptation. It was originally released on January 31, 2014 in Europe and on February 4, 2014 in North America. The album features appearances by singer Howard Jones (ex-Killswitch Engage), rapper Xzibit, metal singer Tarja Turunen (ex-Nightwish), and alternative rock singer Dave Pirner (Soul Asylum). It was the first Within Temptation album to be recorded with three guitarists, with Stefan Helleblad making his Within Temptation studio debut on Hydra after joining the band shortly after the release of The Unforgiving in 2011. Hydra is also the first Within Temptation album to feature Robert Westerholt’s growling techniques since the band’s debut album, Enter in 1997. The band wanted it to be a true Within Temptation album, but heavier, more challenging musically, pushing boundaries with new elements and influences, while at the same time bringing back more of their early metal roots "... a bit like the past and the future at the same time" – as the band stated. The album title refers to the great variety of musical genres, which the band enhances with each new release. Guitarist Robert Westerholt adds: "Hydra is a perfect title for our new album, because like the monster itself, the record represents the many different facets of our music". According to ancient Greek mythology, the Hydra was a giant multi-headed serpent that, for each head cut off, two more would spring up in its place. This new expanded edition comes with 4 bonus tracks.