"Enter the Eternal Fire" was the band's first epic, reaching nearly seven minutes in length, with lyrics referring to a deal with the Devil.

The song "Equimanthorn" makes references to Hell as well as to Norse mythology, including Odin's "eight-legged black stallion" Sleipnir.

Eduardo Rivadavia of AllMusic wrote that the album "remains a career highlight for Bathory, and a crucial LP for all lovers of extreme metal.

He also cited it as a musical inspiration for the 1995 Darkthrone album Panzerfaust, besides Celtic Frost's Morbid Tales and Vader's Necrolust demo.

In 2017, Rolling Stone ranked Under the Sign of the Black Mark as 81st on their list of 'The 100 Greatest Metal Albums of All Time.