Gaby Hoffmann is an altogether fabulous creature who grew up in the Chelsea Hotel before making a lasting impression as the young star of Field of Dreams and Uncle Buck. Her subsequent career has been interesting (Everyone Says I Love You, You Can Count On Me, Perfume, Life During Wartime) but mostly ensemble-driven.

Happily, this thoroughly spaced-out oddity places Hoffmann centre stage, where she most definitely belongs, as the ne plus ultra of the movieverse's Manic Pixie Dream Girl (MPDG) trope. Which is to say more of a Manic Pixie Nightmare Girl. She is a source of constant irritation for Jamie, a paradoxically uptight stoner (Michael Cera), who has little time for Crystal Fairy's propensity for nudity and chakra cleansing.

His hipper, more equable companions (essayed by various Silva brothers) slowly warm to their unconventional fellow-traveller as the group venture across Chile in search of the famed San Pedro hallucinogen. Their odyssey is at once daft and profound, a journey characterised by trippy shenanigans, endless banter and at least one explosive revelation.

Crystal Fairy & The Magical Cactus and 2012 – to give it its full Mayan-themed title – is a fascinating freewheeling DIY doodle guided by improvised dialogue, shaggy diversions and some real-life drug-taking. The film is the brainchild of Sebastián Silva, whose multi-award-winning dramedy The Maid was a 2009 arthouse hit, and it works because the cast brings it.

As with all the best MPDGs, Hoffmann is both disarming and mortifying. The Silva crew are easy company for a long road trip. And Cera invests his best-loved, self-absorbed dork schtick with a fresh spin and surprising depths.

The finished product is roughhewn and odd-shaped. But bacchanalians aren’t supposed to go smoothly.