And that is precisely what they aim for in Tenacious D in The Pick of Destiny, and even when parts of it don’t quite work, you can’t blame them for trying. Black and Gass (who cowrote the screenplay along with director Liam Lynch, who worked with them on the HBO series) go directly for the jugular, giving us the movie equivalent of an overstuffed heavy-metal monstrosity. Bulging at the seams with half-baked ideas (many, I’m sure, written while the duo was fully baked) and an abiding love of all things rock, The Pick of Destiny aims to take its place alongside other rock-fueled cinematic flights of fancy, most of which derive their pleasure from their sheer ludicrousness. The Pick of Destiny comes close, but never quite matches the sheer derangement of something like KISS Meets the Phantom of the Park (1978), if only because we know that Black and Gass are in on the joke, while one has to wonder if the members of KISS had any idea what they were doing.

The Pick of Destiny begins with perhaps its best scene, a rock-opera inspired flashback in which young JB (played by Troy Gentile, who also stood in for a young Jack Black in Nacho Libre) is driven from his ultra-conservative home by his stern, religious father (Meat Loaf) because of his willfully subversive, hard-rockin’ ways. The whole sequence is told in song, with Black’s voice filling the lungs of his youthful alter ego and a poster of Ronnie James Dio coming alive like some kind of twisted spiritual vision. Driven to California (after detours in every other U.S. town named Hollywood), JB meets up with KG (Kyle Gass), who will eventually become his partner in Tenacious D, but not before a lengthy “training sequence” involving the perfection of power slides and other power-rock necessities.

However, in order to become a truly great rock band, the D realize that they must acquire “The Pick of Destiny,” a ghoulish guitar pick they see in the hands of every legend known to rock (from AC/DC’s Angus Young to Eddie Van Halen). They conveniently get the backstory about how the pick was carved out of one of Satan’s teeth from an in-the-know guitar store guru (Ben Stiller, with a perfectly coiffed gray fright wig that says “My life peaked when Ted Nugent was on the Billboard Top 10”). After that, JB and KG head off on their mission to retrieve the pick from the Rock ’n’ Roll History Museum so they can use it to win an open mic night and get money to pay the rent.

The narrative, not surprisingly, is really just an excuse to string together a series of comic and musical setpieces, some of which work better than others. JB’s mushroom-fueled freak-out involving visions of a flying Sasquatch are amusingly absurd, as is their encounter with a towering Goth with a bum leg (Tim Robbins) who wants the Pick of Destiny as badly as they do. Crammed in there we also get parodies of A Clockwork Orange, a Blue Brothers-inspired police chase in a Driver’s Ed Cutlass, and the all-important temporary “break-up” that forces JB and KG to realize how much they need each other (for all the jokiness, there is something endearing about these two portly underdog goofballs feeding off each other’s energy and living out their dreams).

The opening sequence was so good, though, that you wish more of the film had been done rock opera style, rather than keeping so much of the music in the background. The movie does break loose in the climax, though, when JB and KG find themselves in an unexpected “rock off” against Satan himself (Foo Fighters lead Dave Grohl in full Legend make-up). It’s a delirious high point that delivers everything you might hope for both comically and musically, even if the rest of the movie doesn’t quite live up to it.