Question: What kind of group does Necrolust and Celtic Frost have in common?

Context articles: Celtic Frost
Into the Pandemonium
Triptykon
Slaughter (Canadian band)
Necrolust
Septimus Orion
Martin Eric Ain
Apollyon Sun
In Memory of Celtic Frost
Superjoint

Celtic Frost ( ) was a Swiss heavy metal band from Zürich.
 They are known for their strong influence on the extreme metal genres.
 Formed in 1981 as Hellhammer, the band became Celtic Frost in 1984 and was active until 1993.
 It re-formed in 2001 and disbanded following frontman Tom Gabriel Fischer's departure in 2008.
 The band was inspired by heavy metal groups such as Black Sabbath, Judas Priest and Venom, but also by gothic rock acts like Bauhaus, Siouxsie and the Banshees and Christian Death, and by the hardcore punk group Discharge.
Into the Pandemonium is the third studio album by Swiss extreme metal band Celtic Frost, released in 1987.
 The album is more varied than other Celtic Frost's past LPs, with unlikely covers (Wall of Voodoo's "Mexican Radio"), emotionally charged love songs, the album's recurring industrial-influenced rhythmic songs of demons and destruction, traditional Frost-styled songs about dreams and fear, and a dark, classical piece with female vocals.
Triptykon is a Swiss extreme metal band from Zürich, formed in 2008 by Thomas Gabriel Fischer, founding member of the pioneering heavy metal bands Hellhammer, Celtic Frost and Apollyon Sun.
 Fischer announced his departure from Celtic Frost in May 2008 and shortly afterwards revealed his new project would be entitled Triptykon.
Slaughter was a Canadian death/thrash band.
 They formed in Toronto, Ontario, Canada in 1984 playing thrash metal and briefly featured Chuck Schuldiner on guitar in 1986.
 Originally, they released two demos and two full albums. Slaughter was disbanded from 1989-1995 but returned in 1996 to record a cover of Celtic Frost's "Dethroned Emperor" for a tribute album called "In Memory of Celtic Frost".
 In 2001, they re-released "Strappado" under the Nuclear Blast label.
Necrolust is a demo album by the death metal band Vader released in 1989.
 The cover of the album was designed by Piotr Wiwczarek.
 Fenriz of Darkthrone cites this demo along with Celtic Frost's "Morbid Tales" and Bathory's "Under the Sign of the Black Mark" as key riff inspirations for "Panzerfaust".
Septimus Orion is a recording project initiated with the release of its first studio album "CAGED" in August 2008.
 The album includes an audio version of Clifford Meth's short story "Queers".
 This short story was originally published in "god's 15 minutes" by Aardwolf Publishing.
 Celtic Frost drummer Reed St. Mark lends his percussive talents while also working on the Triptykon project with former Celtic Frost band mate Tom Gabriel Fischer.
 Veteran songwriter and musician Mark Radice joined the cast of Septimus Orion while continuing to compose and record for Public Television.
 For this work, Radice was nominated for an Emmy Award in 2008.
 Former front man and vocalist for Lodi hardcore punk band Rosemary's Babies, known as "JR", joined Septimus Orion with a rerecorded version of his song "Sanctioned Violence".
Martin Eric Ain (real name Martin Stricker, born July 18, 1967 in the US) ) is best known for being the former bassist of the influential extreme metal band Celtic Frost.
 He used the stage name Martin Eric Ain throughout his career in Celtic Frost.
Apollyon Sun were an industrial metal band formed by singer/guitarist Tom Gabriel Fischer and guitarist Erol Unala in early 1995, after the termination of Celtic Frost, Fischer's prior group.
 The group was unofficially dissolved in 2001 when Fischer invited Erol Unala to contribute to the reformation of Celtic Frost.
 Their name is taken from the Celtic Frost demo "Under Apollyon's Sun".
In Memory of... Celtic Frost is a Celtic Frost tribute album released in 1996.
 Notable for its inclusion of "Babylon Fell" by Apollyon Sun, which features former Celtic Frost vocalist/guitarist Tom Gabriel Fischer.
 Whilst mostly a tribute to Celtic Frost, it also pays a small nod to Tom Gabriel Fischer's other former band, Hellhammer.
Superjoint, formerly known as Superjoint Ritual, is an American metal band formed by Phil Anselmo, Joe Fazzio, and Jimmy Bower in the early 1990s, later to be joined by Hank Williams III, and Kevin Bond.
 Their style can be considered a mix of Pantera's style of groove metal and hardcore punk.
 A small trace of black metal can be heard, as well.
 Bands like Venom, Slayer, Celtic Frost, Voivod, and Darkthrone have been noted as influences also.