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