[1] The band's hybrid musical style is characterised by heavily distorted guitar riffs, down-tuned rhythms, and vocals ranging from "menacing, echoing" sound effects to death grunts.

[4] Describing the band's style, Decibel magazine said: "If Morbid Angel and Gorguts had birthed a German Expressionist child, that unholy creature would be Portal.

Denise Falzon, writing for Exclaim!, described Portal's 2004 EP, The Sweyy, as "extremely raw [...] with heavily distorted guitar riffs that aid in the album's overall chaotic and apocalyptic atmosphere".

[9]While some critics have noted a "lack of production quality" and "unrefined, murky sound" on Portal's albums,[7] Horror Illogium countered that the band spends considerable time consciously "exploring different equipment for guitar tones with enough articulation as well as dirt".

[9] Stating that "there are only so many frequencies that can share a space," he indicated that Portal's approach involved striking "a balance to allow the instruments to spill forth and explode when necessary.

[10][11] Their costumes are composed of "suits and executioners' masks save for vocalist The Curator", who wears headgear fitting the theme of the latest album, such as "a huge, tattered wizard's hat that obscures his face" in the case of Seepia.

[12][11] The band cites as inspiration for its lyrical themes the entities mentioned in Lovecraft Mythos, such as Nyarlathotep, Yog-Sothoth, Azathoth, and Cthulhu.