I remember reading this book over and over as a child. The protagonist is a bit of a troublemaker, and loves games and jokes. An accident happens (I don't remember what exactly) and he wakes up in a giant board game. Helping him along is a devil his age with horns who introduces himself as Bub, short for Beelzebub. I don't remember exactly how the game worked, but my memory of it is that they move along the edges of the board by rolls of the dice, card draws, or some combination of the two, with obstacles in the game manifesting as actual obstacles. I don't remember if the boy was in any danger from the obstacles, but he seemed pretty carefree about the experience. Near the end of the book, he succeeds in reaching the goal of the board, only to find out that it loops back around, with Bub telling him he's free to just keep playing the game forever. The protagonist is tempted, but gets cold feet, imagining never seeing his family ever again. When he decides to instead go home, Bub sheds his horns and reveals his wings and halo, him actually being the protagonist's guardian angel, who was hoping to get him to turn his life around in this near-death experience.
I believe the cover showed the board game in the background, the protagonist falling toward the board, and Bub looking on with amusement. I think Bub was wearing a beanie with his horns sticking through.