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