Getting special moves:  Quickly collect five cogs to get one letter from the word "SPECIAL" in any level. Keep collecting cogs until the entire word is spelled out. Complete the level to learn a special move.

Defeating Merlock:  When one part of the floor shakes, go to the other part of the floor and dodge the fireballs. The pin-like things being shot from the front are harmless. When he splits up into four forms, hit the one whose pendant glows and repeat. Use caution because the less energy Merlock has, the more floor tiles fall into the lava.

Bonus screen:  Complete 100% of the game (all tasks completed in each level, all costumes unlocked, all special moves unlocked) to view a screen featuring the characters in the game.

Alternate costumes:  For each 10 Golden Threads collected, a new costume for Donald will be unlocked.

Duckie Mountain
Yogabound: Press Up, A(4).
Ring a Ding-Ding: Press Up, X(4).
Soap Opera: Press Up, A, X, A, X.
Pole Pose: Press Up, A, X(2), A

Duckburg.
Soccer Shop: Press Right, A(2), X(2).
Spicy Golf: Press Right, Y(4).
Fab Lifting: Press Right, Y(2), B(2).

Magica's Manor.
Tap Ten: Press Down, Y, B, Y, B.
Ballet Basket: Press Down, B(4).
Stilt Tilt: Press Down, B(2), Y(2).

Getting the Gold Thread:  At some points in the game where there is an obstacle, there is a way through it. To get the thread you will need two things: hyper mode and a breakable object. They are about three of them in each stage. You can see some of them through the path, and others are things that you jumped over.