I mean, you can choose whoever you want, and I’ll do my best. If you pick an isolated creator-owned character that’s going to make for a difficult connection, unless there’s a crossover special, or some historical, living, or public domain figure in there I can use to make one.
Darius (who actually first appeared in Hellblazer) was originally defeated by John Constantine, who is frequently in an on-off relationship with Zatanna, who was deputized as a Lord of Chaos by Mordru, who is an enemy of the Legion of Super-Heroes, who are also enemies of Stargrave.
Stargirl was in the JSA with Doctor Fate, whose helmet was eventually passed down to the 31st century Doctor Fate, who is in the Legion of Super-Heroes with Brainiac-5, who is (allegedly) a descendant of Stargrave.
Extrano was propositioned in DC Pride by John Constantine, who in Trinity War stole the power of Shazam from Billy Batson, who is enrolled in Titans Academy with Stitch.
Byth Rok is the benefactor of Shadow-Thief, who in Joker: Last Laugh was defeated by Cassandra Cain, who was in James Tynion IV’s Gotham Knights with Clayface.
Chas Chandler is the often unwilling chauffeur of John Constantine, who in Tim Seeley’s Hellblazer hooked up with Huntress, who was in the Birds of Prey with Black Canary, who was in Steve Orlando’s Justice League of America with Lobo, who stole Space Cabbie’s cab.
In a Neil Gaiman-written story for 2004’s Solo#8, Deadman infers that Death is his boss.
Lion-Mane was originally an enemy of Hawkman, who was in the JSA with Wildcat, who was an enemy of Tigress.
The Defenestrator was in Section Eight with Sixpack, who drank at Noonan’s with Kyle Rayner, who was in Morrison’s JLA with Wally West, who was in Justice League Europe with Captain Atom, who was the first enemy of Jewelee.