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