To duel Yugi at his grandpa's toy shop, after dueling Arcana, go out of the card shop, & then come back in & challenge the shop's new owner. When you win, leave & go to the toy shop & you will find Yugi. To duel Mai, duel a blue-haired guy at the park. When he asks for information on Yugi, say yes, & then he will agree to duel you. After, he will tell you where Mai is.