Here is the full list of all 9 Once Upon a Jester achievements.
Finish the game!
Steal the Royal Diamond.
Find Pesto.
Pop the frog into popcorn over the campfire.
Make the perfect smikkel.
Unlock all stickers.
Find the fish.
Play the right tune for all Callers during Jerry Jeremy’s radio show performance.
Watch Freek get pulled into the sea by the kraken.