Quietly implicit in the raging successes of SunnO)))’s Black One (last year’s immovable sludge monument) and Boris’s Pink (this year’s suave gut-rock masterpiece) was an inevitable future moment of poignant rock star overreach. Both had conquered with sound and fury; next to come would surely be the nothing-signifying, tale-told-by-a-nü-Metallica twin falls. Who could’ve imagined they’d decide to plunge together? Altar, their much anticipated and soon to be mourned collaboration, rises up—”Etna” builds a dripping meld of SunnO)))’s slasher-flick ominousness and Boris’s depressive flop-sweat into a neck-snapping monster—then collapses. “The Sinking Belle (Blue Sheep),” with its weepy piano balladry and Jesse Sykes–voiced floating melodrama, is a bad Bowie outtake, which makes it far better than “Fried Eagle Mind,” Altar’s five-blunt, drug-soloing nadir. Add Boris guitarist Wata chanting dreeams-style reverie; get reminded of what it felt like to be lifted in junior high. I do dig the Star Wars–copping imperial death march horns of “Akuma No Kuma,” which casts Thrones’ Joe Preston as the track’s raspy, grunting Darth Vader—a time-honored figure of shame and redemption, the latter yet to come.