Here is the full list of all 21 Yu-Gi-Oh! Legacy of the Duelist achievements.
Unlock all avatars
Defeat ZEXAL Campaign
Deal 100k in Effect Damage
Defeat 5Ds Campaign
Win a ranked multiplayer match (duel)
Defeat GX Campaign
Deal 50k in Reflective Damage
Chain 100 times
Win a Battle Pack match (duel)
Perform a Pendulum Summon
Perform a Synchro Summon
Deal 200k in Direct Damage
Perform a Xyz Summon
Create 5 decks
Defeat Classic Campaign
Create your first deck
Perform a Fusion Summon
Win an unranked multiplayer match (duel)
Win a duel by having all Exodia cards in hand
Perform a Tribute Summon
Win all Duelist Challenges