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