In Sonic Shuffle, you can change Lumina into NiGHTS. I found this out from the Technomania section of “Disney Adventures” (April 2001 issue):
“Fool your friends by changing the character of Lumina the fairy into the Nights charatcer (star of the classic Nights game). To do it, go to your Dreamcast's Settings menu and change the date to Christmas Eve, 12/24/00. Then head back to the game and you'll have a whole new character. That's a Christmas present you can use year-round!”
Source: Disney Adventures Magazine