Matthew writes...

1. Does John Constantine exist in the YJ universe

I say this after looking through forty archive questions about King Constantine'a appearance on Gargoyles

2 Could you use him on the show?

I asked this because DC did not let them use Constantine on the old Justice League series. (Though a guy who looks like him appears in the background.) This was partially because at the time they wanted to keep Constantine in his own universe. They also did not want to encourage kids to pick up Hellblazer which is not appropriate for younger readers. Now, though, that Constantine's been brought back into the DC Universe; it might be possible for him to appear on YJ.