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