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