In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: Besides Bathory, Enslaved, and Burzum, several other artists are credited as pioneers of the style. The original bassist for Emperor, Håvard Ellefsen, also known as Mortiis, was "an indispensable force in the genesis of Norway's epic Viking metal sound." Despite Ellefsen's short tenure in the band, it was his musical interests that catalyzed the band to mix chaotic black metal with synthesizer melodies based on Norwegian folk music.Helheim was another major pioneer in the early scene. Helheim emerged on the scene before other bands such as Einherjer and Thyrfing, when even Enslaved was in its infancy. Not only was Helheim one of the first bands to meld black metal with Viking themed-music, but one of the first to include stylistically unconventional instruments such as horns and violins. Robert Müller of Metal Hammer Germany argues that Viking metal never solidified as a genre, and attributes this to Jormundgand, Helheim's 1995 debut album. Jormundgand included an ambitious track – "Galder" – but that song was considered incompatible with metal, and audiences, looking for a specific musical style, merged with the pagan metal scene, which had no particular "Viking" identity.Other highly influential Viking metal bands are Borknagar, Darkwoods My Betrothed, Einherjer, Ensiferum, Moonsorrow, Thyrfing, and Windir. Trafford and Pluskowski regard Einherjer, Moonsorrow, Thyrfing, and Windir as the "most influential" Viking metal bands, with Einherjer's album covers, which include many images of Viking artifacts, giving Einherjer the most Viking feel of all bands except Enslaved. Einherjer's artwork spans the full chronology of Viking art: 8th- and 9th-century Oseberg to 11th- and 12th-century Urnes.
What was the name of the band that mixed the chaotic black metal with synthesizer melodies?