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