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