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