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