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