Apparently, the Bye Bye Man is a malevolent spirit that can be summoned simply by speaking his name only once when that happens, it gets into your mind and causes its victims to see things that aren't really there as a way of driving them to madness and murder.
Other scenes briefly show naked bottoms, a male character appears shirtless, and a female is shown in revealing outfits and underthings. Language isn't frequent but includes a use of "f--k," plus "s--t" and more.