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