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