Unlock Dragon For Free Run
Unlock the Dragon for Free Run by doing all of the following:
In High Jump mode jump higher than 1000ft
Fly through five rings in City Trial
Fly farther than 1300ft in Air Glider

Unlock Extra Characters in Air Ride Mode
Galax - Complete 100 laps on any level.
Meta-Knight - Fly for thirty minutes.
King Dedede - Beat 1000 enemies.
Brown Kirby - Use the wing star to beat Zeroyon Attack 2 under 30 seconds.
Green Kirby - Eat three swordknights and then beat a race.
Purple Kirby - Beat a two-lap race in Airoon under 2 minutes 30 seconds.
White Kirby - Beat a two-lap race in Vallerion under 2 minutes 30 seconds

Unlock Extra Characters in City Trial Mode
Meta-Knight - Destroy 1000 boxes.
King Dedede - Beat King Dedede in Event Stage 24.
Brown Kirby - Use the heavy star to beat Sandoola under 1 minute 30 seconds.
Green Kirby - Use the cannon to destroy an enemy ten times.
Purple Kirby - Destroy an enemy vehicle five times.
White Kirby: - Build the Dragon and the Hydra in one match

Unlock Hydra In Free Run
To unlock the Hydra for free run, do all of the following:
KO 1500 enemies (total) in Kirby Melee
KO your rivals 150 times (total) in Destrution Derby
Destroy all dilapidated houses in City Trial

Hint: Get Off Machine
In city trial mode, hold A to charge up and then hold the control stick down. Kirby will jump off his machine

Hint: Legendary Machine Parts
Look for red boxes in out of the way spots on the track and run over them

Hint: Special Events
In City Trial mode, there are several events that happen where you can do something to gain lots of powerups. Here are some of them:

When the giant U.F.O. comes, go to top of the volcano and cross the bridge, entering the volcano. You will be lifted to a sky tower high above the city. When the U.F.O. flies below the sky tower, drop down onto it and you will find several powerups.

When the giant pillar comes, just destroy it, like it says to.
Whenever Dyna Bird comes, she is always near a ramp. When you have the ability of flight, fly off the ramp and hit her head. Once you've done that enough times, Dyna Bird will fly away, leaving behind many items.

Whenever Tac comes, run into him to make him drop items