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