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