Prometheus says, "One wedding and two funerals."
Cisco refers to Wells as "Squidward."
The Green Arrow appears in part one of a four-part episode that continues on Arrow: Crisis on Earth-X, Part 2 (2017).
The Flash appears in part one of a four-part episode that continues on The Flash: Crisis on Earth-X, Part 3 (2017).
The Legends appear in part one of a four-part episode that concludes in DC's Legends of Tomorrow: Crisis on Earth-X, Part 4 (2017).
Barry reminds Kara that he learned about her ability to sing during their last adventure together.
Nora's interaction with Barry at his and Iris' wedding mentioned
Aiyanna and Heather talk about this special.