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