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