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