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