In the darkness, caught in flashes of light, there's a figure; a clay-coloured nude, leaning back in a chair, two high heels outstretched. Neither male, nor female, half muscular, half obese, it's a body that makes next to no sense, exaggerated out of all proportion. S/he has buttocks like balloons and calves like cliff faces, Chris Hoy's thighs and the sort of bulbous belly, saggy tits combo you see on old women padding around swimming pools in the summer. The head is elephantine. The face is featureless.

In his distended body stocking, Greek performance artist Euripides Laskaridis cuts a bizarre figure – at once intriguing and disconcerting, both comic and awful. He makes a humanoid sculpture, Frankensteinian and unformed; perhaps a statue in progress or just joints of meat stapled together. Tottering around the stage, every footstep echoes like a small earthquake.

Short and mighty strange, Relic is a play on gender and identity. Depending on dress, Laskaridis' mannequin figurine slides between male and female. At one point, in a white sheet, blonde wig and a string of pearls, it seems like a plump well-to-do woman; a posh gallerist giving a gobbledygook speech with a wine glass in hand, perhaps. At another, a black-haired bodybuilder in a pink tinsel bikini morphs into a moustachioed male rocker lashing a whip. S/he'll sit down to pee, draining a sopping sponge onto the floor, then slowly smack a nail into a board. Fluidity isn't the half of it.

Beneath every outfit, there's the same misshapen mess and, at some level, Relic is an expression of our essential, existential selves. There's a marble bust on stage, a very public face, and an out of shape mirror. A large pot plant suggests another layer of outward civilisation. And yet, beneath it all, everyone's shapeless, right? We are all half-human, out of sorts and at odds. We're all uncomfortable in our own skin. "Relic," the programme notes, "is something that has survived the past, something that's left behind." No matter how hard we try to rid ourselves of it or what we do to conceal it, somewhere deep down, the creature in us survives. What is it Prospero says of Caliban? "This thing of darkness, I acknowledge mine."

For all its ugliness, however, Relic isn't as uncomfortable a watch as it needs to be. Kostas Michopoulos's amplified, echoing sound design – sponge-pee like a waterfall, hammer blows like sonic booms – makes great use of fingernails-down-blackboard scratchiness, and Eliza Alexandropoulou's lighting misfires and short circuits, but, once things settle, it's too easy to see a costume, not a creature. Once you're eyes have adjusted, Laskaridis becomes a clown like any other.

Relic runs at the Barbican Centre until 4 February as part of the London International Mime Festival.

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