Here is the full list of all 27 Avatar: The Last Airbender - there are Quest for Balance achievements.
Finish the tutorial.
Use Seismic Sense for the first time.
Use Katara to heal your teammates for the first time.
Block 20 projectiles with your shield.
Launch 20 enemies.
Trap 20 enemies.
Play with a friend (one player as Zuko and the other player as Iroh).
Destroy the cabbage cart 10 times.
Defeat an enemy using Sokka's boomerang to deliver the final blow.
Buy a bending scroll.
Beat story mode.
Beat all the spirit trials.
Find and build all the sculptures.
Beat 3 bosses without getting hit.
Beat all Animal Races with more than 75% of coins collected.
Interact with twenty different objects in the world.
Win all "Beat Momo in a Race" challenges.
Learn the four bending arts with Aang.
Unlock every character.
Defeat Admiral Zhao.
Defeat Zuko and Azula.
Defeat Firelord Ozai.
Defeat a boss with Aang when all perks and bending moves are maxed.
Unlock all character perks.
Find all secret rooms and treasure rooms.
Open all chests.
Finish all side quests.