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