Things start off with Thadeous (Danny McBride) about to be executed by a kingdom of midgets and the film only gets sillier from there when he is forced to accompany his brother Fabious (James Franco) on a quest to save Belladonna (Zooey Deschanel), Fabious’ fiancee who has been captured by the nefarious Leezar (Justin Theroux). Unbeknownst to the brothers, Leezar plans to use Belladonna to fulfill an especially invasive prophecy. As they quest to rescue her, they encounter a perverted wizard, a randy Minotaur and the deadly Isabel (Natalie Portman).

Obviously, a film like this lives and dies on the quality of its jokes. On this front, “Your Highness” has more hits than misses, continuing the “Pineapple Express” method of blending stoner humor, creative cursing and over-the-top violence for laughs. This is a film that may sound like it was written by a 13-year-old, but in the best way possible. It’s raunchy, unapologetic and seems endlessly entertained with itself. Even when the occasional joke flops, there are several far funnier quips quickly following it.

Most of this is thanks to the comedic persona of McBride. After making his film debut in Green’s “All the Real Girls,” McBride has been slowly honing the character he’s best known for: the cocky failure whose ego is matched only by his blissful lack of self-awareness. Coming off of another hilarious season of “Eastbound & Down,” McBride slaps on a preposterous British accent and lends every scene his trademark comedic stylings. If audiences have grown tired of McBride’s schtick, “Your Highness” may be a bit of a chore, but fans will find plenty to laugh at here.

The rest of the cast refuses to let McBride dominate the spotlight, however. Franco’s Fabious is energetic and naive, employing Franco’s goofy smile and natural comedic timing to great effect. Theroux’s detestable wizard almost steals the show, but is segregated from the rest of the cast for most of the film, asked instead to play off of Deschanel’s straight man. When Deschanel is asked to interact with the rest of the cast, she displays an uncharacteristic comedic flair, but mostly flounders in the film’s later scenes, where she’s only asked to look scared and make out with Franco. Portman, on the other hand, is great, taking the filthy, playful persona she brought to “No Strings Attached,” cranking it up, and running with the film’s often ridiculous material. It helps that Portman is given a few action scenes where she proves to be surprisingly badass.

As for director Green, he adapts well to the medieval genre — miles away from the Midwestern, poetic locations where he began making films. Green also displays an adept eye for action sequences, and manages to compose several of the epic landscape shots that defined films such as “Lord of the Rings.”

“Your Highness” is a film that almost defies the rules of logic. A big-budget stoner comedy starring a recent Oscar winner and another nominee that manages to make McBride something of an action hero. By all laws of common sense, this shouldn’t exist. And yet, here it is, in all its shamelessly dirty, hilarious glory, and this weekend, moviegoers will be all the better for it.