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