Question: Mayhem Festival 2015 included a Danish heavy metal musician who was the lead vocalist for what non-namesake band?

Context paragraphs:
Cam Pipes: Cam Pipes is a Canadian heavy metal musician, who performed as the lead vocalist and bassist in the Canadian heavy metal band 3 Inches of Blood.  He performs a falsetto vocal style reminiscent of Udo Dirkschneider and King Diamond.  Pipes was the only member of 3 Inches of Blood to have been featured on all of their albums, although he was not a founding member of the band.

King Diamond: Kim Bendix Petersen (born 14 June 1956), better known by his stage name King Diamond, is a Danish heavy metal musician.  As a vocalist, he is known for his extensive vocal range, in particular his usage of falsetto.  He is the lead vocalist for both Mercyful Fate and the eponymous King Diamond.

Mayhem Festival 2015: Mayhem Festival 2015 was the eighth and final annual Mayhem Festival.  It was confirmed that Slayer, King Diamond, Hellyeah and The Devil Wears Prada will be headlining the festival, while Whitechapel, Thy Art Is Murder, Jungle Rot and Sister Sin would be among those supporting.  Dates were announced on April 13, 2015.

Eizo Sakamoto: Eizo Sakamoto (坂本 英三 , Sakamoto Eizō ) is a Japanese heavy metal musician who was born in Nishinomiya, Hyōgo Prefecture.  He is most famous for being the lead vocalist of 1980s band Anthem.  In the 1990s he started up the band Animetal which performed heavy metal covers of anime and tokusatsu opening and closing themes.  He also was involved with the anison supergroup JAM Project before reuniting with Anthem.  Sakamoto then began a new project called "Eizo Japan" which is similar to Animetal: more heavy metal covers of theme songs post-disbanding, along with original material.

Mayhem Festival: The Mayhem Festival was a touring heavy metal festival that took place during the summer.  The inaugural season took place in 2008; the festival has since become an annual event across the United States.  Most years also include a single date in either Montreal or Toronto, Canada.  The tour has been sponsored by the Rockstar Energy Company since the time of its inception.  It was assembled by Vans Warped Tour founder Kevin Lyman, and by John Reese (who was Lyman's partner on the Taste of Chaos tour).  On August 2, 2015, Reese confirmed that the 2015 festival would be the last one.

Volbeat: Volbeat are a Danish heavy metal band formed in Copenhagen in 2001.  They play a fusion of rock and roll, heavy metal and rockabilly.  They are inspired by classic rock and roll artists such as Elvis Presley and Johnny Cash, as well as modern hard rock, thrash metal, heavy metal, alternative rock and hardcore punk groups.  Their current line-up consists of vocalist and guitarist Michael Poulsen, guitarist Rob Caggiano, drummer Jon Larsen and bassist Kaspar Boye Larsen.  The band is signed to Dutch label Mascot Records and has released six studio albums and one DVD.  All of their studio albums have been certified gold in Denmark.  Their second album "Rock the Rebel/Metal the Devil" received platinum status, and their 2010 release "Beyond Hell/Above Heaven" was subject to widespread international critical acclaim, receiving double platinum in Denmark, platinum in Finland and Germany, and gold in the United States, Sweden and Austria.  Volbeat's sixth album entitled "Seal the Deal & Let's Boogie" was released worldwide on 3 June 2016.

Uproar Festival: The Uproar Festival, also called the Rockstar Energy Drink Uproar Festival, was an annual hard rock and heavy metal tour inaugurated in 2010 by John Reese and sponsored by Rockstar Energy Drink.  The tour was also created by John Oakes, Darryl Eaton and Ryan Harlacher from the Creative Artists Agency, and Perry Lavoisne from Live Nation.  Reese is also responsible for creating Mayhem Festival and the Taste of Chaos tour.  Uproar Festival is the replacement for Reese's Taste of Chaos tour, as he was "running out of bands that fit within the profile of what Taste of Chaos was."

Mayhem Festival 2011: The heavy metal music tour, Mayhem Festival 2011, was the fourth annual Mayhem Festival created by Kevin Lyman.  The official lineup was announced on January 31, 2011.  It was the first year that the festival utilized a rotating main stage slot, and the first year that the tour had more than one act returning from previous lineups.

Insidiöus Törment: Insidiöus Törment, also referred to as IT or (misspelled) Insidious Torment, is a Danish heavy metal band with Soviet roots.  The heavy metal umlaut in their band name, a usually purely decorative device, is actually pronounced.  In heavy metal, a musical genre that is sometimes described as "proto-fascist", the group is also known for being one of the few overtly socialist bands, along with some other notable examples, such as Accept.  Like Accept in the lyrics to "Balls to the Wall", Insidiöus Törment also call for the oppressed to rise and rebel in such songs as "Metal Balls", "The Enticer" and "Call to Arms".

Mayhem Festival 2010: Mayhem Festival 2010 was the third annual Mayhem Festival created by Kevin Lyman.  The 2010 edition of the festival was co-headlined by Korn and Rob Zombie.  As in previous years, the main sponsor of the festival is Rockstar Energy drink, and each date had a different Battle of the Bands winner performing on the Jägermeister stage.  In addition to three stages with various heavy metal bands, Mayhem Festival 2010 also hosted other entertainment acts.  As in previous years, the Freestyle Motocross stunt team Metal Mulisha returned, in addition to comedian Jay Oakerson and a costume party/variety act "Beacher's Madhouse" featuring DJ's and the scantily-clad "Beacher's Babies".

Supporting paragraphs: Mayhem Festival 2015 King Diamond
Answer: Mercyful Fate