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