Unlock the following costumes for your Mii by performing the corresponding tasks:

COSTUME - HOW TO UNLOCK
Big The Cat Suit - Play 3 Hours
Charmy Costume - Play for over one hour.
Chip Outfit - Play for over 5 hours in Events
Cream Outfit - Get 1st Place in 10 London Party Bonus Games
Diddy Kong Suit - Play against a friend 20 times in Single Event Mode.
Emerl suit - 50 answers right in the london party quiz
Espio Costume - Come in 1st Place 10 times.
Iggy Suit - Play as a Mii in 50 Events
Larry Suit - Answer 10 questions right in London Party quizzes.
Lemmy Koopa Suit - Answer 100 questions right in London Party quizzes.
Ludwig Koopa Suit - Play against a friend 10 times in Single Event Mode.
Marine Suit - Get 1st Place in 50 London Party Bonus Games.
Morton Suit - Play as a Mii in 100 Events
Roy Koopa Suit - Answer 50 questions right in London Party quizzes.
Super Sonic Suit - Get 50 1st places
Tikal Suit - 1st place in over 100 london party events
Toad Suit - Play against a friend 5 times in Single Event Mode.
Wendy Koopa Outfit - Play as a Mii in 10 Events
Werehog Suit - Come in 1st Place 25 times.