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