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