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