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