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