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