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