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