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