If you're looking for manga similar to Dream Eater Merry, you might like these titles.
Excessive sleepiness never seems like letting Nattsu, the 14-years old boy has a normal dream. Every time his eyes shut, his world changes into a cloudy dimension with bizarre creatures and strange humans. What is exactly Nattsu's purpose in that world? Why does he keep getting more drowsy? Will someday our MC found out why he was called "Mr. Dreamnotes"?
Nightmares are bad enough when asleep, but In Dream World, nightmares are real, physical monsters! Drake, Hanee, and Kyle fight these Nightmares with not only weapons, but "In Dream Cards". These cards have different elemental powers, and those who wield the cards are masters of their elements. Hanee and her friends must battle their way through the land of Nightmares to find their way home.
High school teenager discovers by chance that he has the ability to control dreams and pull others into his dreams.
A girl has the ability to visit a surreal alternate dimension full of monsters in her dreams. One day, she encounters another human girl there and receives a plea for help.
Amahashi Miku is a first year student at the elite Mifuta Academy, and it's a perfect one. Suddenly her life changes when she is chosen to play a role on the academy play. Soon a lot of events happen, including supernatural ones...and she even starts to have strange dreams with a unique black cat...