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