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