Halloween comes but once a year, so it’s appropriate, on this spooky special occasion, that doom wizards Acid King grace us with a rare San Francisco appearance — just two days before the most metal of holidays! Founded in 1993 by guitarist/singer Lori S. and drummer Joey Osbourne, Acid King has endured a host of line-up changes and label switches, but the core of the band’s sound hasn’t changed much, subsisting on steady diet of tectonic, down-tuned riffsmithing, thrumming leads, and Lori’s otherwordly vocals.

Can’t say I’m sure which drummer or which bassist will show up at the Hemlock, but the uncertainty shouldn’t deter you — their respective pedigrees are guaranteed to be impeccable. The music on offer will combine suet-thick sludge and shimmying fuzz, representing a masterful take on the kind of languorous ‘luded-out Sabbath-worship that fans of the genre know and love.

Openers Christian Mistress are rapidly rising through the ranks, and the buzzed-about Olympia, WA quintet seem to have the talent to justify their meteoric ascension. Their relentlessly retro NWOBHM sound turns the clock back to the heyday of Maiden and Priest, though the brassy vocals of singer Christine Davis add an unexpected, modern touch. Mini-LP Agony & Opium is wall-to-wall headbanger bliss, and the group is likely to debut new material on this tour.

Thrones will headline, offering a thunderous conclusion to an all-round barnstormer of a bill. Former Earth, Melvins, High on Fire, and Sunn O))) bassist Joe Preston’s solo project offers a wide-variety of skull-crushing, psychedelic excursions, and you never really know what he’ll do next, except that it will be extremely heavy. Armed with a bass and synthesizer, he’ll make war on your eardrums.

Hemlock is doing a double bill on the 29th, so the awesome won’t start until 9:30 PM. Get there early, though — there aren’t any online pre-sales, and Acid King hardly ever plays live. All the hard info lies below:

Thrones, Acid King, Christian Mistress
9:30pm, $10
Hemlock Tavern
1131 Polk St., SF