Here is the full list of all 27 OkunoKA Madness achievements.
Defeat the Fairy Bugs boss
Defeat the Desert Plains boss
Defeat the Space Impacts boss
Complete the story
Eat the blue spirit for the first time
Eat the red spirit for the first time
Eat the yellow spirit for the first time
Complete all levels in Madness world
Eat a spirit for the first time
Respawn more than 30 times
Unlock the first whirlwind
Get your first 'S'
Complete all whirlwinds
Finish a level without dying once
Die by hitting a thorn
Die by being struck by a laser
Die by being hit by a missile
Complete a race at Fairy Bugs without dying in Time Attack mode
Complete a race at Desert Plains without dying in Time Attack mode
Complete a race at Space Impacts without dying in Time Attack mode
Complete a race at Vulcano's Bay without dying in Time Attack mode
Complete a race at Madness without dying in Time Attack mode
Complete all levels in all worlds with a score of S
Complete all levels in all worlds with a score greater than A
Unlock all characters
Eat all purple spirits
Finish the game at 100%