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