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