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