Search:

Have Star Wars ever had a crossover with another property? I guess you can count the time Luke Skywalker appeared on the Muppet Show, but I can't think of other examples.

Also John Constantine appears in Mobfire, a Vertigo miniseries from 1994.

The version of Bob, the Galactic Bum where Lobo appears. (Some versions, not published by DC, replace him with another character.)

John Constantine works better as a foil to more colorful characters. On his own he's just another '90s sadsack.

Not my favorite but...

The Legion of the Super-Heroes time travel in the year 4016 and find out that the Legion has evolved into a sinister Illuminati-type secret society.