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