Here is the full list of all 39 LEGO The Hobbit achievements. It takes around 35-40 hours to unlock all of the achievements on Windows.
Play a level in co-op
Collect 10,000,000,000 studs. (Single Player Only)
Equip yourself with Dazzle Wig, Mithril Rhythm Stick and Mithril Dance Boots.
Complete the Bonus Level
Achieve 100% completion
Collect all characters. (Single Player Only)
Complete all the quests in Middle-earth. (Single Player Only)
Forge all the Mithril Treasure Items. (Single Player Only)
Forge all the Perfect Mithril Treasure Items. (Single Player Only)
Collect all Mithril Bricks. (Single Player Only)
Use Gandalf's startle ability to dazzle 50 enemies
Collect all Schematics. (Single Player Only)
Create a custom character.
Transform to Beorn's bear form.
Equip Thorin with the Mithril Mushroom Crown
Complete ''Queer Lodgings''
Complete ''Out of the Frying Pan…''
Complete ''The Troll Hoard''
Complete ''Over Hill and Under Hill''
Complete ''Roast Mutton''
Complete ''Azog the Defiler''
Use every Dwarf from Thorin's Company in a Buddy-Up attack
Use 50 Buddy-Up attacks
Complete ''An Unexpected Party''
Complete ''Greatest Kingdom in Middle-earth''
Obtain all Master Burglar titles. (Single Player Only)
Complete the mining game perfectly 50 times
Collect all Minikits. (Single Player Only)
Collect all Treasure Items in levels. (Single Player Only)
Complete ''Goblin Town''
Complete ''Inside Information''
Complete ''On the Doorstep''
Obtain 150,000 studs from Instruction Builds bonuses. (Single Player Only)
Complete ''The Necromancer''
Complete ''Looking for Proof''
Complete ''A Warm Welcome''
Complete ''Barrels Out of Bond''
Complete ''Flies and Spiders''
Collect 99 of any loot