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