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