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