"Arrow" season 4 will bring back John Constantine, at least for one episode. This particular episode is where Sara Lance will ultimately be resurrected. Executive producer Wendy Mericle recently told IGN how this could play out. 

"It was born more out of the storyline for Sara Lance. We needed someone to come in and help bring her back. He felt like the most exciting possibility and we're just thrilled to get him. He brings such a different element to the show," the EP said. 

Constantine will appear in "Arrow" season 4 exactly how he was in his own show. And although the small screen universes of Oliver Queen and Constantine are going to be merged, there are no promises of more appearances as his inclusion is more of a necessity. 

Meanwhile, Sara's resurrection, according to TV Line, isn't something her family actually needs right now, knowing that Captain Lance (Paul Blackthorne) is just learning to move on from his daughter's death. 

"Thanks to Laurel helping him see the light at the end of last season, Lance is back on the wagon for now, trying to keep on the straight and narrow," Blackthorne said, as quoted by the aforementioned publication. "But that will of course be tested when Sara comes back from the dead. Because I think when your daughter's coming back from the dead, she may not necessarily come back as quite the same person. Yeah, that's going to be an issue for the family to deal with."  

Meanwhile, Oliver's new lair was recently unveiled. There is space where Felicity can do her tech magic, where Oliver can work out, and there is a garage. There is also more space to discover as the season progresses.

"Arrow" season 4 will premiere on Oct. 7.