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