Pierrot is the tenth Cardian that Alan and Ann (more precisely Alan) send to gather energy for the Doom Tree. She has the appearance of a clown and attacks with an umbrella to drain energy. She can also have the umbrella extend a cord to wrap around her victims. She appeared in Sailor Moon R Episode 10, Mirror, Mirror on the Wall.
During the Snow White and the Seven Dwarfs play, in which Darien was Prince Charming and Ann was Snow White (with the intent of kissing Darien), Alan, partly out of disappointment that he did not get the part of Prince Charming (so he could kiss Serena, who in turn did not get the part of Snow White), and partly to gather energy for the Doom Tree, sent Pierrot to crash the play and drain energy from the audience. Pierrot even threw a giant ball at Ann to knock her backwards, and Darien caught her as she fell, though his nose was hit in the process. Serena transformed into Sailor Moon, but Pierrot attacked her with her umbrella, until the Moonlight Knight arrived. The other Sailor Scouts appeared, and Sailor Mars threw a scroll attack onto her face, and she was then frozen by Sailor Mecury's Mercury Ice Bubbles Freeze. Sailor Moon proceeded to destroy Pierrot with her scepter.
Pierrot looks like Pennywise from Stephen King's It.
The way she attacks with an umbrella is similar to the Penguin from Batman.