Nightfall doesn't work with the current build of Skylanders. She works with an update for some consoles. She will not work currently on a Wii and possibly 3DS.
Question: My Nightfall toy is not registering in Skylanders SuperChargers. What's happening?
Answer: Since the launch of Skylanders in 2011, Activision has been committed to delivering high-quality toys to our consumers. It has come to our attention that our software is unable to recognize the Skylanders SuperChargers Dark Element character Nightfall. As a result, we stopped the shipment of the majority of the toys before they arrived at retail. We will be reissuing the toy as soon as possible, and consumers should find Nightfall on shelves before the end of the year.
If you have received a non-functional version of the Nightfall toy, please call 1-844-HELP-EON for assistance from Activision. We sincerely apologize for any inconvenience this may cause Skylanders fans.