Spoilers ahead for Part 3 of the Arrow-verse's "Crisis on Infinite Earths" crossover on The CW.
The long-awaited "Crisis on Infinite Earths" crossover was hyped for the better part of a year as an event tying The CW's five Arrow-verse shows together to fight a common enemy, with a sixth show joining the fold when Black Lightning's Jefferson Pierce was pulled to Earth-1 and DC Universe's Titans getting a cameo in the first part. As it turns out, however, the crossover stood to get a lot more devilish thanks to the appearance of a star from yet another still-ongoing DC Comics-based show: Lucifer. And it may have delivered a big reveal for Lucifer's final season on Netflix.
Despite Lucifer star Tom Ellis going the extra mile to debunk rumors that he would appear in the "Crisis" crossover (via ET), he showed up at his devilish best when Constantine, Mia, and Diggle arrived on Earth-666 to ask help for getting to Purgatory and restore Oliver's soul after his dip in the Lazarus Pit. Aside from the perfection that Lucifer is evidently set on Earth-666 in the Arrow-verse, Lucifer's comments to Constantine suggest that Constantine could have a part to play in Lucifer Season 5 on Netflix.
Lucifer wasn't too eager to help Constantine and Co. in the quest to get to Purgatory, but he agreed to assist because he owed Constantine for Maze. Neither Lucifer nor Constantine got into specifics of what Constantine did for Maze, but we do know that Lucifer Season 5 is slated to go into Maze's backstory. In fact, Tom Ellis revealed that Season 5 will feature a storyline that is "the genesis of the Maze that fans have come to know and love."
Did the appearance of Tom Ellis as Lucifer in "Crisis" confirm that he and Maze got the assist of a popular DC hero at some point in the past? And did it reveal that an appearance from Matt Ryan as Constantine in Lucifer isn't out of the question?
Honestly, if any Arrow-verse character is going to cross over to a streaming service show, I feel like it should be Constantine. After Constantine was cancelled by NBC, he jumped to Arrow on The CW (and took a shot at NBC in the process), after which he became a regular on Legends of Tomorrow. Why not appear on Netflix's Lucifer? Considering Season 4 ended with Lucifer stuck back in his role as King of Hell, Constantine could even serve a purpose beyond whatever he did to help out Maze.
Lucifer and Constantine agreed that they were square with each other after Lucifer gave them Arrow-verse heroes a way to get Oliver to Purgatory, so neither has a free favor to cash in with the other at the moment. Still, if "Crisis on Infinite Earths" can pack in all that it has packed in so far, I'm not going to rule out anything when it comes to DC TV. In a fun nod to Lucifer's Amenadiel, Lucifer also declared that Diggle reminded him of his brother.