The masked individual attacked a 19-year-old in the eastern city of Rostock on Thursday, leaving him with bruises to the head and arms, police said.
Four other assaults or scares were reported in the region the same day.
A 15-year-old was threatened by a creepy clown with a knife at a bus stop, also in Rostock. The teen fled and was not injured.
In nearby Greifswald, two children aged eight and 13 were frightened in separate incidents by three clowns, including one with a chainsaw, and a woman had a frightening encounter with a clown who apparently wielded the same weapon.
Around a dozen other cases have been reported around Germany over the last week, according to Bild daily.
The phenomenon has spread to Europe from the United States, with Sweden last week reporting a case in which a man was stabbed by an attacker wearing a clown mask.
"The fear is that clown attacks will become a very, very ugly trend that could spread in big cities in the run-up to Halloween," the head of Germany's police union, Rainer Wendt told Huffington Post.
"These clowns are not only idiots, they are offenders," Wendt said.
He called on victims to report any cases and for judges to "impose the highest sentences, and that can be a jail term of several years," in order to quell the trend.