7) Spectre
Those who watched the short-lived Constantine (which was revealed to take place in the Arrowverse when Matt Ryan’s John Constantine appeared in Arrow’s fourth season) may recall that a supporting character on that show was cop Jim Corrigan. DC fans will know that Corrigan goes onto become the supernatural hero the Spectre in the comics. However, even they might have missed that this eventuality was teased on the show.
In the episode “Danse Vaudou,” psychic Zed Martin has a vision of Corrigan’s future where he is riddled with blood and bullet holes and surrounded by a green mist. This mirrors the character’s origin story from the comics, in which he is killed but his soul is sent back to his body by a higher power to rid the world of evil. While it’s a nice nod to Spectre, it’s still frustrating that this particular arc was left unexplored and we’re hopeful for an appearance by the character in the near future.