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