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