Most of the Achievements are not missable.
Ready to fly! is unlocked at the beginning of the game.
MISSABLE: After your catapult is complete, aim too high for Good Thinking #1 and Good Thinking #2
Making Gold, Sword Bearer, and Made Something Special are all unlocked while completing the first quest. After completing the first quest, you unlock Adventurer.
Navigator and Something Of A Fairy Tale are unlocked while looking for the Wizard.
Egg Stealer, Legal Drinking, and Got Feather are part of the second quest, but it is possible to unlock them before meeting the wizard.
Got Root is part of the second quest, but cannot be unlocked until you have met the wizard.
MISSABLE: While in the graveyard, try to get the root BEFORE putting the clean mirror in the statue’s hands. A ghost should scare you away, earning you Let’s get going!.
Chapter 3 and Finale
Watch your head, Sweet Dreams, Lets Celebrate!, Wedding Crashers, and Game Completed are not missable.
MISSABLE: There she is! may be missable. After getting the invisibility potion, use the knife on the robot toy and the clock face to get two cogs. place the cogs in the knight’s gauntlet in the empty room. Look through the holes in the portrait.