Here is the full list of all 25 DreamWorks Dragons: Legends of The Nine Realms achievements.
Complete the King's Realm
Unlock all Crystal Beacons
Complete the King's Realm in Challenge difficulty
Fully upgrade Thunder
Fully upgrade the whole team
Fully upgrade Wu & Wei
Fully upgrade Plowhorn
Fully upgrade Feathers
Complete the Dark Realm
Complete the Dark Realm in Challenge difficulty
Get 500 Orange Gems
Make 500 enemies escape
Complete the Fire Realm in Challenge difficulty
Complete the Ice Realm in Challenge difficulty
Get 500 Purple Gems
Complete the Bioluminiscent Realm in Challenge difficulty
Obtain your first Orange Gem
Feathers has joined the team!
Get 500 Blue Gems
Wu & Wei have joined the team!
Obtain your first Purple Gem
Plowhorn has joined the team!
Unlock your first ability
Complete the first level
Obtain your first Blue Gem