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