Anybody remember horror-core hip-hop? Of course not. The morbid subgenre flared up in the mid-’90s, spawned some inspired acts (Gravediggaz), along with some lifeless ones (Flatlinerz), and just as quickly turned to ash. Clearly, Chicago production duo The Opus remember that moment with fondness: Though they thankfully forgo horror-core’s gimmicky, death-obsessed lyrics, their instrumental sophomore album is as bleak and intimidating as any tale Brotha Lynch Hung ever spun. But for all its hip-hop noir, the darkly ethereal ”Breathing Lessons” (Mush) is surprisingly easy listening, thanks in no small part to Mr. Echoes’ and partner The Isle of Weight’s persistent percussion programming. You’ll find yourself nodding right along even as multiple layers of droning chords and eerie half melodies loom like ominous clouds on the horizon. Call it good mood music for bad moods.