why is it call 'monsters ball'

It is a term used to describe the night before a prisoner is executed. It is the last celebration before his or her death.

Well, it's a stretch, but these people had monstrous qualities, and Hank was looking for redemption, Leticia needed to be rescued, from her point of view it's a bit of a Cinderella story, she at the end is gazing at the stars feeling like perhaps her husband and son, she looked at Hanks graves? Were looking down upon her, at peace knowing she was going to be ok. She was nearly in the street when she is saved, given a car, her coach, treated like a princess in ways she never had before, she was finally at the ball. She even didn't have her shoes on when she started to drive, they had no reason to tell us that. If I've learned one thing studying movies, no lines are wasted, nothing they show has no meaning, well in good films like this one anyway! No filler. I think the title was used to figuratively describe the characters and the story line. It is the name of the night before an execution ceremony thing and all, but I think they used the name of that to say the monsters were at peace and finally he'd overcome his tyrant and was becoming a loving 'prince' in the neighbourhood while she was a fable kind of female, who would now be taken care of, for her, in a palace by comparison. There's a magic in the air for her at the end, whereas he is at peace and says, I think we're going to be ok... It's a happily ever after done really well. No sentimentalist nonsense.

Well since it's explained in the film, this is obviously a troll post.

Poorly Lived and Poorly Died, Poorly Buried and No One Cried