The Sandman was a villain from The Real Ghostbusters cartoon series and was rather unique in the fact he was not truly malevolent, rather he was misguided and sought to end war and suffering via putting the entire human race into a 500 year old slumber.
The Sandman made his debut in"Mr. Sandman, Dream Me a Dream", where he was on a mission to stop all war by putting all of mankind to sleep for 500 years. He wished to do this in order to stop all wars and create peaceful world where dreams only exist. He put many people to sleep, and their wild dreams caused much chaos throughout the streets of New York. These actions attracted the Ghostbusters to his doorstep. He managed to put all but Winston to sleep.
Winston finally learned that if people realized that what they saw were a dream, they could take control of what was in their dream. Winston rushed back and laid a trap for the Sandman at headquarters, which was successful when Janine got the drop on the Sandman by dreaming she was a Ghostbuster and her dream self successfully managed to halt the Sandman. Winston then delivered another blast and Slimer successfully trapped the Sandman. After he was captured, all his victims were awakened.
As a Sandman, the Sandman's powers all are based on sleep. He wields a blowgun that he uses to blow dust onto people. When a victim is put to sleep, the visions within a dream are brought to life. He can also change these dreams into nightmares. He also has the ability to teleport away whenever someone tries to attack him, letting him escape harm to prepare a counter-attack.
The flaw to his powers is that if a victim realizes that it's only a dream, they can take control of the visions. He doesn't seem to be aware of this flaw as he simply considers anyone who is asleep no longer a threat, which ultimately led to his defeat.