Here is the full list of all 29 Dream achievements.
Finish Act Three's Nightmare.
Finish Act Three.
Visit all the side dreams.
Finish Act Two.
Finish Act Two's Nightmare.
Eat all the cupcakes.
Finish Act One's Nightmare.
Finish Act One.
Finish the graveyard puzzle in ten moves or less.
Find the memories of an old experiment.
Find a past project.
Epic support needed...
Show off your festive side.
Collect all the Dream bible pages.
Play the first bar of 'Counting Sheep'.
Leave on all the lights before sleeping.
Find the mess on floor one.
Finish all four mazes without getting caught.