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