According to my informant, El Cucuy was a creature similar to the boogeyman with a red cape, fiery eyes , sharp teeth and sharp claws. In the middle of the night, if you were a child wandering in the streets, you were not supposed to be found by him. He would often hang out in a plaza and try to void his presence. If he ever caught a child, he would take him to his cave, where there would be many skulls and dismembered limbs. This was what remained of the kids he captured before. And nobody would ever know what happened to the children because they never returned.
My informant described this as a story to scare rowdy children into obedience. It also, he joked, made for a very good horror story with all the blood and mystery that happens. But more seriously, he also said that this story was told to him by his mother when he was a kid. Being someone who grew up a Mexican-American, this story scared him as a child and he always obeyed his parents.
This story reflects some elements of La Gerona, in that it is a story which is used to tame unruly children and make sure they respect the words of their elders. There also happens to be death involved when they get caught. But I feel that the main difference between the two is that while La Gerona is more sympathetic and tragic, El Cucuy seems to be more psychopathic and more intentionally killing children. This factor makes the story much more chilling than La Gerona, instilling more fear into the child the person is talking to. I think that this story seems to be a little exaggerated, especially the addition of the red cape, which seems superfluous. But since this story was told by his parents, I assume that this was a feature which was recently added either by the informant, who tends to exaggerate a bit, or by his parents.