Here is the full list of all 18 King's Heir: Rise to the Throne achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Find all the Collectibles in the Main Story.
Pet all the animals, even if they run away.
Finish a Hidden Object Puzzle in less than 20 seconds.
Finish a Minigame in less than 30 seconds.
Find all the Collectibles in the Bonus Chapter.
Finish a Fight Minigame without making a mistake.
Place the crown on Randall's head.
Finish the final Fight Minigame without using Skip.
Finish all the Hidden Object Puzzles without using Hint.
Take a moment for a tankard of liquor.
Feed the animals, big and small.
Take a leap of faith into the water.
Find half of all Collectibles in the Main Story.
Finish 3 Hidden Object Puzzles without using Hint.
Finish the Lock Picking Minigame without using Skip.
Finish a Hidden Object Puzzle with less than 3 mistakes.
Finish the first Fight Minigame without using Skip.
Find the first Collectible.