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