6) Doctor Fate
It might have only run for 13 episodes but Constantine managed to tease the existence of not one but two significant heroes in the Arrowverse. Alongside the vision of the Spectre, the series teased another figure with one fateful easter egg.
In pilot episode “Non Asylum Est,” Liv Aberdine picks up a rusted golden helmet. Fans will immediately recognize this as the Helmet of Fate – one of the most powerful objects in the DC universe which bestows magical powers on whoever wears it. In the comics, the helmet has been worn by multiple heroes who take up the mantle of Doctor Fate.
Fate previously appeared on Smallville and, as it doesn’t seem likely that the movies would use this fairly obscure character, let’s hope that the Arroverse introduces himself properly at some point.