At the "Press Start" screen, press Up(2), Down(2), Left, Right, Left, Right, Circle, X(2) at the "Press Start" screen. All skins will now be available at the "Unlockables" menu.
Secret Damage Moves:
Damage the following Bosses with the corresponding techniques. Defeat the boss, then the next level will then be in Hard mode.
BOSS - MOVE
Wolf Robot - Reflect his dynamite back at his face.
Wolf King - Wait for him to stand on top of a breakable floor block. Hit him until laughs, then drill attack the floor so that he falls.
Axel Gear - Have him get hit by the tracking purple ball attack that he uses.
Gold Sparkster mode:
Complete Arcade mode under the Hard difficulty setting, using the secret damage move on every Boss.
Unlock the following skins by performing the corresponding tasks:
SKIN - HOW TO UNLOCK
Axel Gear - Complete Arcade mode under the Hard difficulty, using the secret damage move on every Boss.
Gold Sparkster - Complete Gold Sparkster mode.
Burst Friends - Defeat 5 enemies in a single Rocket Burst or Drill attack.
Elhorn Tourist - Completed all stages.
Ferocious Flier - Completed 1.2 having defeated all enemies.
Nimble Knight - Completed 3.2 without taking damage.
Wolf Connoisseur - Completed 2.1 having collected all pickups.
Woodland Bouncer - Defeat 3 enemies with a single reflected projectile.
Zephyrus Saviour - Completed Arcade Mode on Normal.
Devotindos Defiler - Completed Arcade Mode on Hard in a Single Playthrough.
Impatient Hero - Completed all stages below par time.
Redoubtable Runner - Completed Arcade Mode on Hard within 60 minutes.
Spark Dog Millionaire - Completed Arcade Mode scoring One Million Points or more.
Legendary Possom - Completed Gold Sparkster Mode.