Pause game play, then press R, X, L, Y, Up, Right, Left, Down.
Cow headgear
Pause game play, then press L, R, Y, X, Left, Down, Left, Right.
Detective outfit
Pause game play, then press Left, Right, Left, Right, Left, Right.
Essences
Essences can be found at the indicated locations.
Leaf Essence: Tree stumps, your houses, and Torajiro's house.
Fire Essence: Cool Trees and Roy's furniture store.
Heart Essence: Lovely Trees and phone booths.
Water Essence: Fountains.
Diamond Essence: Kayaking race course in the Mangrove Forest.
Star Essence: Lamp posts and Lovely House 2.
Brown Diamond Essence: Flowers and the Town Hall.
Bubble Essence: The Curio Shops and the snowman from the Synth-O-Matic.
Moon Essence: Dr. F's Laboratory and the Heliport.
Question Mark Essence: Garbage cans and the Gondola Summit.
Planet Essence: The ski slope, stone pillar, and slide.
Patchwork clothes
Pause game play, then press Right, Down, Left, Up, L, R, L, R.
Patchwork pants
Pause game play, then press Down, L, Left, R, Up, Y, Right, X.
Punk bottom
Pause game play, then press Left, R, L, Right, Y(2), X(2).
Punk top
Pause game play, then press Up, X, Down, Y, Left, L, Right, R.
Samurai armor
Pause game play, then press Y, X, Right, Left, L, R, Down, Up.
Samurai helmet
Pause game play, then press X, Y, R, L, X, Y, R, L.