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