I think this extract from the Mixed language's wikipedia article will help you:
Different from a pidgin:
A mixed language differs from a pidgin in that the speakers developing the language are fluent, even native, speakers of both languages, whereas a pidgin develops when groups of people with little knowledge of each other's languages come into contact and have need of a basic communication system, as for trade, but do not have enough contact to learn each other's language.
Different from a creole:
In a mixed language, both source languages are clearly identifiable. This differs from a creole language, which generally has one identifiable parent, in addition to diverse input which cannot be traced to any particular language. While creoles tend to have drastically simplified morphologies, mixed languages often retain the inflectional complexities of both parent languages.