Here is the full list of all 119 Torchlight II achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Sell 50,000 items
Defeat the Nether King with each of the 4 classes
Defeat the Nether King as an Embermage
Defeat the Nether King in Elite difficulty
Defeat the Nether King as an Engineer
Defeat the Nether King in hardcore mode (elite)
Defeat the Nether King in Veteran difficulty
Defeat the Nether King in hardcore mode (veteran)
Defeat the Nether King as an Outlander
Use 5,000 potions
Defeat the Nether King in hardcore mode (normal)
Defeat the Nether King in hardcore mode (casual)
Socket 500 gems into items
Have 50 friends
Destroy 100 socketed gems
Use an enchanter 500 times
Purchase 100 items from the gambler
Purchase 50 items from the gambler
Purchase 20 items from the gambler
Destroy 10 socketed gems
Recover 100 gems from items
Have 10 friends
Trade an item with another player
Fish 1,000 times
Have 10,000,000 gold
Die with a hardcore character
Start a hardcore character
Deal 100,000 critical strikes
Use 100 maps
Find 100 secret rooms
Defeat Aleera
Defeat Verona
Defeat Marishka
Assemble TrillBot
Break 10,000 breakables
Start a multiplayer game
Add a friend
Join a multiplayer game
Have 1,000,000 gold
Reach level 100
Use 500 potions
Teach a pet 4 spells
Teach a pet a spell
Obtain a tier 3 skill bonus
Find a legendary item
Recover 10 gems from items
Sell 5,000 items
Squish 1000 critters
Defeat 500 champions
Socket 50 gems into items
Defeat Grand Regent Eldrayn
Use 50 potions
Defeat Chillhoof
Defeat King Pogg
Defeat Kidrik the Mauler
Begin new game plus
Use 10 maps
Fish using dynamite
Find 10 secret rooms
Take 100,000 steps
Recover a gem from an item
Squish 500 critters
Explode 10,000 enemies
Use a map
Defeat the Nether King as a Berserker
Defeat the Nether King in Casual difficulty
Defeat the Nether King in Normal difficulty
Defeat the Nether King
Defeat the Dark Alchemist
Defeat Killbot
Defeat Vyrax
Do 10,000 damage with a single attack
Defeat Thiss
Use an enchanter 50 times
Defeat Cacklespit
Deal 10,000 critical strikes
Fish 100 times
Defeat Bloatfang
Defeat the Grizzled Alpha
Defeat the Wraith Lord
Defeat Boletus Rex
Obtain a tier 2 skill bonus
Defeat the Siege Guardian
Break 1,000 breakables
Open 500 chests
Defeat Ezrek Khan
Take 50,000 steps
Destroy a socketed gem
Defeat Aruk
Defeat the King In Masks
Defeat 100 champions
Use an enchanter 10 times
Defeat the Artificer
Sell 500 items
Have 100,000 gold
Squish 100 critters
Defeat the Manticore's Mate
Defeat the Manticore
Deal 1,000 critical strikes
Learn 4 spells
Explode 1,000 enemies
Defeat 25 champions
Defeat the Winter Widow
Defeat General Grell
Take 10,000 steps
Wear a completed armor set
Obtain a tier 1 skill bonus
Open 100 chests
Find a secret room
Send your pet to town
Learn a spell
Fish 10 times
Defeat One-Eyed Willy
Socket a gem into an item
Defeat Mordrox
Break 100 breakables
Defeat the Fallen Guardian
Open 20 chests
Explode 100 enemies