Nightmare is the entity that the inhabitants (ones with duties) of Wonderland sees in their dreams. He has the ability to read one's thoughts/heart.
He is the citizen of the Country of Clovers.
"I am a dream demon, the embodiment of bad dreams." --Nightmare (Direct quote from official manga)
Alice in the Country of Hearts: Wonderful Wonder World
This is the movie based on the Alice in the Country of Hearts otome games.