Black Lady was the form Chibiusa took when she was turned to evil 由 Wiseman.

Anime

In the anime, Chibiusa travelled to the future with the Sailor Senshi and once there, heard King Endymion tell them that the Silver Crystal disappeared shortly before the Black Moon Clan attacked.

Thinking that it was her fault that the Crystal vanished, and thus her mother was hurt, she became upset and ran away, leaving the shield around the Crystal Palace. Wiseman found her there and began 展示 her illusions that made her think that everyone blamed her for what happened. He told her that he could convince...

Dark Mercury, who has also been referred to 由 the unofficial nicknames of Darkury 或者 Dark Sailor Mercury outside of the series, was the evil form of Sailor Mercury who appeared only in Pretty Guardian Sailor Moon. She first appeared in Act 21, after Sailor Mercury was kidnapped and brainwashed 由 Kunzite.
At first, she appeared like a normal, but 冷却器 Ami (dubbed "Akumi" (悪美; meaning "Evil Beauty") 由 the series production staff). But shortly thereafter she transformed into Dark Mercury, much to the horror of the other Sailor Senshi.
She was often disrespectful toward Kunzite and the other...