Unless you’re a band with 14 years of mind-meld chemistry under your belt, under no circumstances should you attempt what Horrendous are going for on their fifth album. The Philly death metal vets have a history of shapeshifting—witness their gradual transformation from OSDM revivalists to progged-out fusion heads between 2012’s The Chills and 2018’s Idol—but this is by far their brashest play yet. In under 40 minutes, Ontological Mysterium gallups, grinds, and glistens through an array of seemingly unrelated death metal subsects, even venturing beyond the genre for the occasional melodic interlude. It’s tempting to view this as a culmination that Horrendous have been building toward, but the freewheeling spirit and outright fun of Ontological Mysterium make it the band’s most drastic departure to date.

With its emphasis on momentum and melody over technical prowess, the wide-open, triumphant intro track “The Blaze” might make you think you’ve accidentally pressed play on an atmospheric black metal classic like Agalloch’s Ashes Against the Grain. Oddly enough, Ontological Mysterium’s other biggest outlier is its delirious closer, “The Death Knell Ringeth,” a lizard-brained groove metal banger that completely counters the methodical opener. In between, Horrendous return to their signature brand of progressive death metal, jam-packing it with more solos, non-sequitur song structures, and unrestrained experimentation than ever. After three albums of ruthless precision and studied evolution—2014 breakout Ecdysis, 2015’s Anareta, and Idol—the eclecticism comes as a shock.

In an interview, guitarist/vocalist Matt Knox explained the new album’s stylistic sweep as a way to “encapsulate everything we’ve ever done.” Indeed, you can hear the strains of doom that crept into Ecdysis on “Preterition Hymn,” the catchy, Symbolic-era Death worship of Anareta on “Chrysopoeia (The Archaeology of Dawn),” and the jazzy, fretless bass-led tones of Idol on “Aurora Neoterica.” But the frenzied way they’ve arranged and sequenced the songs has no precedent in the Horrendous catalog. In this regard, Ontological Mysterium channels an uninhibited energy, a no-holds-barred ethos that runs counter to the careful curation of the band’s past work. When, at the very end of the album, second guitarist/vocalist Damian Herring bellows, “Time is too fucking short,” you might wonder if “carpe diem” was the original creative prompt.

The willingness to pull out all the stops is apparent in Ontological Mysterium’s virtuosic musicianship, but its heightened sense of freedom also brings out Horrendous’ inner metal goofball. It’s hard to imagine the younger, more self-serious incarnation of this band indulging in this album’s pulpy horror and campy riffage. Even Knox has acknowledged that, in the pursuit of different vocal approaches, the band wound up with some that were “completely absurd”—see the “Iron Man”-esque intro of “Exeg(en)esis” or the Peter Steele-style clean baritone that pops up in “Chrysopoeia (The Archaeology of Dawn).”

Despite all of the eye-popping pyrotechnics, the members of Horrendous know when to stay out of each other’s way—the second Herring or Knox start to run counter to the song’s groove, the rhythm section falls into lockstep and bassist Alex Kulick picks up the melodic backbone. When Kulick’s neck slides and Jamie Knox’s drum fills pave the way for the breakdown on “The Death Knell Ringeth,” both guitarists hang back and play rhythm parts. The Knox brothers have been playing with Herring and a rotating cast of bassists since 2009 (Kulick came onboard full-time for Idol), and their innate coordination as songwriters enables them to throw out the subgenre-specific blueprints past albums relied on. For Horrendous, who have always been a workmanlike unit of death metal perfectionists, the whirlwind approach is a breath of fresh air.

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Horrendous: Ontological Mysterium