Here is the full list of all 97 Trine 2: Complete Story achievements. It takes around 35-40 hours to unlock all of the achievements on Windows.
Complete Cloudy Isles
Find all secret chests in Cloudy Isles
Complete Brackenridge Rise
Find all secret chests in Brackenridge Rise
Complete Belly of the Beast
Find all secret chests in Belly of the Beast
Complete Deadly Dustland
Complete The Heroes Return
Collect all experience pickups in Petrified Tree
Complete The Story Begins
Complete Forlorn Wilderness
Complete Mudwater Dale
Complete Mosslight Marsh
Complete Petrified Tree
Complete Shadowed Halls
Complete Hushing Grove
Complete Mushroom Caves
Complete Mushroom Murk
Complete Searock Castle
Complete Eldritch Passages
Complete Icewarden Keep
Complete The Final Chapter
Collect all experience pickups in The Story Begins
Collect all experience pickups in Mudwater Dale
Collect all experience pickups in Shadowed Halls
Collect all experience pickups in Mushroom Murk
Find all chests in Forlorn Wilderness
Find all chests in Mudwater Dale
Find all chests in Mosslight Marsh
Find all chests in Petrified Tree
Find all chests in Shadowed Halls
Find all chests in Hushing Grove
Find all chests in Mushroom Caves
Find all chests in Mushroom Murk
Find all chests in Searock Castle
Find all chests in Eldritch Passages
Find all chests in Icewarden Keep
Find all chests in The Final Chapter
Collect all experience pickups in any level
Find all chests in the game
Complete the game
Kill an enemy with a thrown hammer bouncing at least once before kill
Feed carnivorous plants with three or more different kinds of treats
Shoot 3 arrows in the air and catch them all with the Knight's shield
Get at least 10 enemies killed by other enemies' actions in a single level
Stand on a conjured box bouncing on any bouncy surface for 10 seconds
Stand on a plank floating on a single airflow for four seconds
Make a bubble sink for three seconds
Make goblins die of three different environmental hazards in a single level
Complete a whole level playing one character only
Shatter three frozen enemies within one second
Construct a tower made of eight objects and stand on top of it
Using grapple, swing around an object and reattach grapple again without touching any surface
Earn all (original) Achievements in Trine 2
Collect all experience pickups in Forlorn Wilderness
Collect all experience pickups in Mosslight Marsh
Collect all experience pickups in Hushing Grove
Collect all experience pickups in Mushroom Caves
Collect all experience pickups in Searock Castle
Collect all experience pickups in Eldritch Passages
Collect all experience pickups in Icewarden Keep
Collect all experience pickups in the game
Freeze two enemies and stack them on top of each other
Complete any level with hardcore mode on and difficulty set to hard
Complete the game on hard using hardcore mode
Complete a level with only Amadeus
Complete a level with only Zoya
Complete a level with only Pontius
Complete a level with only Amadeus, a level with only Zoya and a level with only Pontius
Kill an enemy with an airborne object tossed with the Knight's charge
Finish a level without taking any damage (Not the Tutorial)
Build a three-piece or three-character tower where lowest part is Pontius and his shield, tower must stand at least five seconds
Complete Goblin Machinations
Collect all level experience in The Heroes Return
Collect all level experience in Deadly Dustland
Collect all level experience in Belly of the Beast
Collect all level experience in Brackenridge Rise
Collect all level experience in Cloudy Isles
Find all chests in the Goblin Menace expansion
Find all level experience in any level in the expansion
Collect all level experience in the Goblin Menace expansion
Earn all Achievements in Trine 2: The Goblin Menace
Capture three different types of enemies inside boxes and stack them on top of another
Collect all experience pickups in both the main game and the Goblin Menace expansion
Kill a grenadier goblin with its own cannonball
Make a sandworm kill another sandworm
Launch an object with Knight's magnetic shield and break it with hammer before the object touches the ground
Complete any level of the Goblin Menace expansion with hardcore mode on and difficulty set to hard
Complete each expansion level using only one character
Complete the Goblin Menace expansion on hard using hardcore mode
Throw a box with Pontius' magnetic shield and catch it or have another player catch it
Create a makeshift raft of three separate parts and have a goblin sail it for five seconds
Glide for five seconds with Kitesail Shield while having an object or character on top of the shield
Kick five enemies of the same kind into a bottomless pit with the Thief's grappling hook kick or the Knight's Kitesail Shield glide kick
Capture a goblin in a Monster Prison and then launch it with a catapult
Find all secret chests in The Heroes Return
Find all secret chests in Deadly Dustland