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