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