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