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