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