The golden sarcophagus that traps Cyrus Borg is the same one the Serpentine tried to steal in Season 1, Episode 10 ("Child's Play").
Nya confront the new, mysterious Samurai X in the museum. [S7E3] A Time of Traitors
The episode marks the introduction of the Vermillion commanders: Blunck, Raggmunk, and Machia. The golden sarcophagus that traps Cyrus Borg is
Nya fights possessed samurai armor at the museum while investigating the Vermillion's activities. More details on the Time Twins' history ? A summary of what happens in the next episode ? "Ninjago" A Time of Traitors (TV Episode 2017) - IMDb [S7E3] A Time of Traitors
Kai’s vision of his parents isn't a true flashback, but rather his mind’s interpretation of the scene, which explains why baby Nya is wearing her modern Water Ninja attire.