Quite often you’ll see a trailer that doesn’t do justice to the film it’s advertising. Maybe it’s tonally wrong, or it gives too much away, or the music is off. There are hundreds of potential failings, and it happens a lot. Much more rare, though, is a film that doesn’t do justice to its trailer. Fatman is one of those films.

If you saw it, you’ll know that the Fatman trailer was nothing short of amazing. It was a masterpiece of mood, showing a grizzled, bearded Mel Gibson toiling away on a farm in the snow and preparing to defend himself against an unknown invader. When the reveal comes – and we learn that Gibson’s character is actually none other than Santa Claus – it lands with timing perfect enough to take your breath away. It was the sort of trailer that made you scroll back to the start to double-check that it wasn’t a lost SNL sketch. It was beautiful.

Sadly, though, the trailer deserves to be seen as the definitive version of Fatman. The actual film is an hour and a half longer, but every additional second feels like padding. To watch the whole thing is to watch a really good gimmick wander off and get lost in the snow. And this is a real shame because, if handled correctly, Fatman could have helped to reinvigorate Mel Gibson’s career. But as it stands, it is destined to go down as just another curio, to be filed alongside The Beaver and Machete Kills as an example of Gibson’s post-Sugar-tits flailing.

The story, what there is of it, is a sort of vaguely Trumpy satire about a rich little boy who, when he receives a lump of coal one Christmas morning, orders a hit on Santa. The assassin he hires is an extremely self-aware Walton Goggins, spectacularly out-Gogginsing himself as a man with his own reasons for wanting Santa dead.

Not that this is a Santa who particularly wants to be alive. He’s sour and drunk and broke and entirely devoid of Christmas spirit, commercially outpaced by sweatshops and raging that he’s “full of a loathing for a world that’s forgotten”. So with this in mind, casting Gibson actually seems like a pretty smart decision. As an actor, he lost his chance. He’ll never be Mel Gibson: Movie Star again, and he knows it. It bleeds out of him. And so his Santa is just as curdled and ruined as we expect Gibson the man to be. When we encounter him closeup, his face etched deep with all the crevices that a decade of rage will give you, it feels like the closest that he will ever come to autobiography.

The problem is, though, that Fatman just doesn’t go anywhere. After setting Goggins on a collision course with Santa, the film simply leaves them both to twist in the wind. It might be pitched as a First Blood-style battle of wits between two worthy adversaries, but that isn’t what this film is at all. This is a film about Walton Goggins slowly learning where Mel Gibson lives, and that’s it. There is no sense of inevitability whatsoever. The pair of them don’t meet until the final 15 minutes and, when they do, it’s the first time that Santa even knows about an assassination attempt. The final fight itself is over in a matter of seconds. And while it’s pleasingly bloodthirsty in places – this may well be the only film ever made to feature a scene where Santa Claus drools blood – it feels hollow and anticlimactic.

You assume that Fatman was designed to be remembered as a cult Christmas classic in the vein of Bad Santa but, if that was the case, it falls well short. The world in which it takes place is well enough realised, but the story is broad and formulaic, as if it was dashed off in a panic. It might look violent and gritty but, in truth, Fatman has more in common with a mass-produced Hallmark holiday movie that it would like you to believe.

• Fatman is released in the US on 13 November with a UK date to be announced