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