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