The Flash Season 6 Review: 8 Ups & 2 Downs From 'Crisis On Infinite Earths, Part 3'
7. Better The Devil You Know
John Constantine's task to help Mia and Diggle retrieve Oliver's soul from Purgatory required him to reach out to an old friend. That friend just so happened to be Earth-666's Lucifer Morningstar.
The surprise appearance of Lucifer's Tom Ellis was unexpected to say the least. Yes, if you'd been up to date with all the leaks, you might have remembered that it was coming, but as it was one of the less publicized appearances, you could be forgiven for missing it.
Not only did this confirm the existence of Lucifer in the wider Arrowverse, it gave fans the chance to see Ellis' devil and Matt Ryan's Constantine share a scene together - something we'd been longing to see for quite some time. From the fact that they knew each other, to their quick-witted exchange, it was a scene worth waiting for, and an absolutely genius use of the Lucifer character that never once felt gratuitous.