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