You can have me almost every night, Sometimes I could be bad sometimes I can be nice, Whether you were a child or an adult i'll be there. What am I?

“A nightmare”

While a nightmare is a type of dream that can be considered 'bad', the riddle refers to a broader category that includes both good and bad experiences, not just the negative aspect.

“Sleep”

Sleep is the state during which dreams occur, but the riddle specifically asks for something that can be had almost every night, which more accurately describes a dream itself rather than the act of sleeping.

“A movie”

Although movies can be enjoyed almost every night and may evoke various feelings, they are not something that is universally experienced by everyone every night like dreams.