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