S2·E48 Ms. Yuri's Mission

When Ms. Mari witnesses the apparent death of Ms. Yuri, she reveals the truth about her twin sister that she was separated from at a young age. However, Ms. Yuri returns to life and is ordered to kill her sister. She takes Misaki hostage and reveals that she's a superhuman descendant of Duo, an intergalactic force that will soon arrive on Earth. Lan and the kids intervene and try to stop Ms. Yuri who uses a Dark SynchroChip to fight, but she is swayed against Nebula. In the end, Dark ProtoMan appears and strikes, presumably killing both Ms. Yuri and Misaki.