Question: Which Danish heavy metal band from Copenhagen released a compilation album of rare demo tracks?
Context: Mercyful Fate is a Danish heavy metal band from Copenhagen, formed in 1981 by vocalist King Diamond and guitarist Hank Shermann.  Influenced by progressive rock and hard rock, with lyrics dealing with Satan and the occult, Mercyful Fate were part of the first wave of black metal in the early to mid-1980s.  Many of the bands from this movement went on to influence later black metal musicians in the 1990s, particularly in Norway.  Since the band's inception in 1981, Mercyful Fate have released seven studio albums, two extended plays and four compilations. Pavour Nocturnus is the first EP by the Australian hard rock band Behind Crimson Eyes, released in 2005.  It is the band's debut official release, as the only thing that came before this EP was a rare demo from 2004.  Along with the demo and following EP , Pavour Nocturnus saw re-release on the compilation album Scream Out Your Name To The Night.  The words "pavour nocturnus" roughly translate to "night terrors". Return of the Vampire is a compilation album of rare demo tracks by Mercyful Fate recorded before their first, official release in 1982.  It is released in 1992 by Roadrunner Records RRD 9184. Never, Neverland is the second album by heavy metal band Annihilator.  It was released on September 12, 1990 under the label Roadrunner.  The album was re-released twice: 1998 with 3 demo tracks as bonus tracks and again on September 9, 2003 in a two-disc compilation set along with "Alice in Hell", entitled "Alice in Hell/Never Neverland" (as part of Roadrunner Records "Two from the Vault" series). Somewhere in the Swamps of Jersey is a 2006 release from Lifetime.  This two-disc compilation album is a collection of early singles, covers, demos, compilation tracks, live tracks and two versions (one remixed and one remastered) of the band's first album, "Background".  Disc one contains the singles and demo tracks along with the remixed version of "Background", while disc two contains the remastered recording and a live set.  The release also includes a 52-page book of liner notes, lyrics and over 40 rare photographs. Beneath... Between... Beyond... is a compilation album released in 2004 by the band Static-X.  It is a compilation of previously unreleased tracks, remixes, cover versions, and the band's original demo tracks.  A track with the same title appeared as a bonus track on iTunes version of the band's album "Cannibal", released three years later. Capricorn One: Singles & Rarities is a compilation album by the Santa Cruz, California-based punk rock band Good Riddance, released through Fat Wreck Chords July 6, 2010, three years after the band's breakup.  The tracks on the album span 1993 to 2006 and include songs from Good Riddance's "Gidget" and "Decoy" EPs and their split releases with Reliance, Ignite, Ill Repute, and Ensign, as well as three tracks from Fat Wreck Chords compilations and six previously unreleased demo tracks.  All of the tracks were digitally remastered by Jason Livermore at The Blasting Room.  The compilation is titled after the 1978 film "Capricorn One", about a Mars landing hoax.  The album's liner notes include Rankin's lyrics and comments on each song. 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. Embryonics is a double-CD compilation of tracks by the Australian progressive metal band, Alchemist.  It was released in 2005 in Australia by Chatterbox Records and worldwide by Relapse Records.  The album features 28 tracks recorded by the band between 1990 and 1998 including eight songs from the album "Jar of Kingdom", eight from "Lunasphere" and five from "Spiritech" along with a cover of "Eve of the War" from "Jeff Wayne's Musical Version of The War of the Worlds" that was the title track from EP "Eve of the War" that is now deleted.  The live version of "Chinese Whispers" is also from that EP; the other live tracks were recorded in 1995 at the studios of Triple J for an episode of "Three Hours of Power" and are exclusive to this release.  "Paisley Bieurr" and "Imagination Flower" are early demo tracks. Mirage was a heavy metal band which was formed in 1983 from the ashes of two Welsh Rock/ Metal bands: 'Rough Justice' and 'Exit'.  The band were based in the valleys of South East Wales, UK.  Its members were Richard Morgan (aka "Wretch) on vocals, Richard Price on guitar, Carl Skinner on bass and Gerry Turner on drums.  In 1984, they released one track 'Blind Fury' on a compilation album produced by local record company 'Notepad Productions'.  This came to the attention of Malc Macmillan, author of the Encyclopaedia of New Wave of British Heavy Metal (NWoBHM) who described their track 'Blind Fury' as "truly one of the classic tracks of the entire NWoBHM genre" The rare Notepad Productions VOLUME I album remains highly sought after by collectors - featured in Record Collector Magazine in January 2015.  The band has enjoyed some recent attention from High Roller Records who have re-released the band's tracks Blind Fury/ Twilight Zone on black and white vinyl.  The cover features Richard Price's original 1979 Fender Stratocaster guitar alongside a Turner family artefact from World War II.
Answer: Mercyful Fate