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