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