This is the premise of 13 Sins. A salesman named Elliot Brindle (Mark Webber) loses his job a couple of days before his marriage, which is unfortunate because he's already in debt and has a baby on the way. Lucky thing, then, that he starts getting these phone calls from a mysterious voice (George Coe), offering increasingly high rewards for completing increasingly sociopathic challenges. He can walk away from any challenge without consequence, but he'll lose all the money he's made before.
You can see exactly where this is going: as the game progresses, Elliot's tasks will become more dangerous, and have greater consequences for those around him.
It's surprising, then, that 13 Sins managed to hold my interest for its duration. That's because the movie doesn't quite go as far as one expects; you're expecting Elliot to become a homicidal monster, and for the police to be closing in as he pulls the pin on a grenade just before the credits. This doesn't happen, though. Instead, the plot complicates. Elliot's family gets involved. A police detective (Ron Perlman) has a vague idea that this game has been played before, and is trying to put an end to it. Finally, it appears that there may be other people playing the game as well.
If 13 Sins does one thing well, it keeps Elliot human. Horror movies are populated by horrible people whose only functional purpose is to die in a satisfying way, but these characters are deliberately unsympathetic. I find slasher movies difficult to penetrate because I don't like any of the characters. Elliot, on the other hand, is bland but relatable, and there's an unexpected moment where he finds that he's enjoying himself, and we find that we're enjoying the ride. And all the while we know that there's an abrupt end coming.
I enjoyed 13 Sins, and I'm curious about 13 Beloved, the Thai film on which it is based, but my understanding is that writer/director David Stamm took great advantage of the carte blanche he was given to rewrite the plot. I'm afraid that this might be one case where the imitation is more inspired than the original.
Here's the trailer.