5) Oracle
Of all the characters that make up the Batfamily, it might seem odd that the only one categorically confirmed to exist in the Arrowverse is Barbara Gordon AKA Oracle. This must be the case, though, as she was namechecked by Green Arrow himself.
In season four episode “A.W.O.L.,” Oliver gives Felicity the nickname Overwatch. However, he says that he would prefer to call her Oracle, but can’t because the name is already “taken.” Of course, this is a reference to how Felicity’s role – a wheelchair-bound tech genius – mirrors Oracle’s.
On a related note, another Batman sidekick who might exist in the Arrowverse is Dick Grayson. Bludhaven has been referenced before, which is the city Grayson protects in his guise as Nightwing. A boy can also be glimpsed wearing a classic Robin costume at Halloween in an episode of Constantine.