The oft-asserted wisdom behind the categories "Fringe" and "Mainstream" runs something like this: the mainstream is mainstream because it is more fun, while the fringe is the fringe because it's so unremittingly serious its arty eyebrows disappear up its own fundament.

As those who read Ms TN with attention will know, she is a mortal enemy to these categories. Because one needs some kind of general handle, I prefer the slightly less unsatisfactory "main stage" and "independent" for distinguishing between companies with large institutional structures and those running on rags and hope, and I certainly never use them as aesthetic predictors or descriptors. Otherwise you fall into absurdities, such as Peter Craven's and Robin Usher's claims a few years ago that artists such as Jérôme Bel or Romeo Castellucci - who have played some of the largest venues in Europe - are "anti-mainstream". Whatever that means.

Anyway, the point is that fun occurs, or doesn't occur, across the entire spectrum of theatre. (Actually, "fun" is a depressing word, which for me evokes the spectre of cocktails with suggestive names in bleakly desperate nightclubs, or The Footy Show, or a certain scoutmaster I once encountered who had an extraordinary talent for killing any kind of social enjoyment by shouting: "Now everybody listen! We're all supposed to be having fun here! Will the mums stop chatting and line up so we can wrap them in toilet paper, ok? We're all having fun! Ok?")

There's "pleasure". Or "delight". Spontaneous joy. Whatever. It's a lightness of being that rises involuntarily and lifts us momentarily out of time on a gust of laughter. Like happiness, it can't be commanded - which is why that scoutmaster got it so wrong, and why it's so sheerly embarrassing to watch a bad comedian. In such moments of delight, we forget the weight of ourselves. We become bigger than we are, and more innocent; we might gasp at comic savagery, but our souls are never shrivelled by its calling to our meaner selves. So while the Sam Newmans of this world might claim they're "just having a bit of fun" by saying black people are just like monkeys, they never inspire delight. Sam's just saying he's the biggest boot on the block, and his obsequious followers snigger in the bully's shadow.

True delight is liberation rather than such enslavement. For instance, on Friday I spent five hours at La Mama, at Moira Finucane and Jackie Smith's Triple Bill of Wild Delight! (It comes with an exclamation mark). On a balmy autumn evening, the moon swinging high over our heads, it was hard to think of anywhere better to be. We arrived to find La Mama's courtyard decked out as a cantina, with coloured lights and candle-lit tables, serving pre-show sangria and barbecued corn cobs and chorizos, before being ushered into Finucane's one-woman storytelling fantasia, The Feast of Argentina Gina Catalina. Argentina Gina Catalina is - well, what is she? Her footsteps melt the pavement where she walks; her deadly gaze can freeze the hearts of two thousand pirates; she's the daughter of wolves and whales and a priestess who can make a cascade of oranges fall out of the sun. She is the embodiment of excess and desire, and she carries the tropes of magical realism beyond parody, into sheer hilarious poetry.

Finucane's performance is as over-the-top as her gorgeous costumes; she ignites a spectacle of desire that somehow, for all its excess, unwaveringly maintains its own reality. Duende, maybe? The sensuality of the language takes cliche and sets it on fire; even as our credulity is mischievously mocked by more and more outrageously absurd stories, we believe in Argentina Gina Catalina. In between each narrative, we're fed and watered with various delicious titbits: olives, bread, Spanish cured meats, mussels steamed in boullibaise, chocolate cake, ice cream and tequila (the food is provided by KT Prescott).

After a half hour's break in the Pleasure Garden, there's contemporary circus with Azaria Universe, Jesse Love and Derek Ives in Tooth & Nail: a show with trapeze and aerial acts (astounding in La Mama - who would have thought it?) in which the traditional circus tropes - especially the sexy showgirl - are undermined, mocked and also brilliantly realised. We still, after all, want to see deeds of derring do, even if the co-stars are bickering and putting razor-blades in each other's toffee apples. The final act, in which the naked performers stand before us wearing huge cartoon animal heads, is so blazingly strange that it knocks the performance into some other dimension. Perverse, disturbing and oddly beautiful.

And after that comes Salon de Dance DELUGE, hosted by Maude Davey, which features an all-star cast of performers mainly drawn from Melbourne's rich dance scene. It features 19 acts, performed inside and outside La Mama; they range from the absurd (two identical Frauleins with blond pigtails performing a bawdy version of the lederhosen slapping dance, or Moira Finucane, dressed as a prim waitress, orgasmically eating a meat pie to AC/DC's TNT) to the beautiful (Brian Lucas, performing a dance of yearning as he rises operatically from a sea of red fabric) to the macabre (Yumi Umiumare's weeping, faceless woman dancing in a dark forest, or Finacune's later adventures with a sauce bottle, as excruciating a performance of sexual loneliness as anything I've seen). Or there's Christopher Green's recital of Molly Bloom, as you've never heard it before, which gives us, as he points out, some "proper acting". As, indeed, it does.

Everything is directed with unobtrusive slickness: food is served, theatres re-dressed, costumes changed, tomato sauce mopped, with never a glitch in the action. Stage manager Cath Carmody must be working harder than anyone else in Melbourne. She and her staff of enablers, plus the first-class performers, add up to a show that reminds us why life is worth living. It's wit, poetry, hilarity, nonsense, pleasure, beauty, all rolled into a gloriously subversive, wickedly sexy evening that nourishes both soul and body. You can book each show separately, but I recommend seeing the lot if you possibly can. Long live Finucane and Smith, I say.

The night before, your fearless correspondent was pursuing pleasure at the Collingwood Underground Carpark. Plunging like a dark mouth beneath the tower blocks of Collingwood, it seems at first glance an unlikely venue for seekers of delight: but enter past the forbidding portal, and you are in another world, possibly Berlin circa 1984, where gorgeous denizens of the underworld gather around an incongruously cosy bar, as music blares at a decibel level beyond the range of the human ear.

The occasion here was Sisters Grimm's production of Little Mercy. At the proper time - or, to be more accurate, a little after the proper time - audience members were led along a path in the darkness marked out, like an airport landing strip, by rows of candles, to a surprisingly intimate theatre scratched together somewhere in the bowels of the carpark.

Little Mercy is an absurdity devised by Declan Greene and Ash Flanders, a fond pisstake of that staple of Hollywood horror movies, the demon child. Roger Summers (Sean-James Murphy) and his wife Virginia (Ash Flanders) are the successful power couple: he is a celebrated musical director, his wife a successful glamour alcoholic. There is only one grief in their life: they have no child. As the play opens, they are rushing off to the premiere of Annie when Virginia (searching for her earrings) discovers a letter from an orphanage mysteriously left beneath a couch. Just as she reads the contents, lightning flashes, thunder rolls and the child itself, Mercy (Susie Dee, in frilly dress and pigtails) appears at their front door.

A carnivorous cuckoo, Mercy settles into the house and begins her murderous career by killing the adored but ancient cat (a stuffed toy which scuttles in and out of the stage on a skateboard) and blinding her tutor (Cara Mitchell) by substituting sulphuric acid for her eye drops. The one difference from the Hollywood version is that, instead of being sent back to the Abyss from whence she came, Mercy wins the day.

It's acted with the appropriate po-faced melodramatic passion by its cast, with some ingenious stage tricks and multi-media. In some ways, it recalls The Thirty Nine Steps, which the MTC produced in 2008: it has the same light hearted delight in meta-theatrical camp, the same low-tech pleasures. And the production and performances are high quality, with Ash Flanders as the soft-hearted innocent Virginia stealing the night, so by the end I wholly believed his performance. Nonsense, yes, but irresistibly funny nonsense, delivered with brio and flair.

Finucane & Smith's Triple Bill of Wild Delight: The Feast of Argentina Gina Catalina, Salon de Dance DELUGE and Tooth & Nail. Devised by Moira Finucane and Jackie Smith, with numerous collaborators. La Mama Theatre, until March 28. Check the La Mama website for details of performance times.

Little Mercy, by Ash Flanders and Declan Greene, directed by Declan Greene. Costume design by Alice Swing, lighting design by Katie Sfetkidis, print media design by Andrew Downer. With Ash Flanders, Cara Mitchell, Sean-James Murphy and Susie Dee. Sisters Grimm @ Collingwood Underground Carpark, 48 Harmsworth St, Collingwood, until March 27. Bookings: Sisters Grimm.