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