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