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