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