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