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