Given Arrows ever-expanding roster of characters and guest stars, you never know whos going to turn up next. As such, it was a pleasant surprise to many to see John Constantine appear in Season 4s fifth episode, Haunted. Matt Ryan did wonders as the titular lead in NBCs Constantine series, yet the show was cancelled after one season despite positive reactions from critics and fans alike. And with that cancellation, it was believed that was the last wed see of Ryans Hellblazer. During the island flashbacks, we see Baron Reiter torturing an unknown man, but its only when we hear the familiar Constantine score and the roguish faux scouse accent that we realise that its John Constantine who is the latest person to take a trip to Lian Yu. Over the course of the episode, both in flashback form and in present day Star City, wed see Constantine and Oliver Queen become BFFs as Hellblazer plays a key role in helping to stabilise the mind of the resurrected Sara Lance.