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