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