For a playful, mischievous rascal:
* Tagata leaga (literally "bad person," but used playfully)
* Tagata valea (literally "foolish person," but used playfully)
* Tupu leaga (literally "bad child," but used playfully)
For a more serious, troublesome rascal:
* Tagata leaga (this can have a more serious connotation)
* Tagata solitulafono (literally "criminal")
* Tagata leaga i le mafaufau (literally "evil-minded person")
Ultimately, the best translation depends on the specific context and the personality you want to portray. It's always helpful to use descriptive phrases to give a more complete picture.