JoshuaLapinBertone: Denise Howard was the sister-in-law of Terra, who was on the Teen Titans with Cyborg, who was later on the Teen Titans with Superboy, whose talent manager was Rex Leech.
Redhood.55520: Negative Man was in the Air Force with Hal Jordan, who was on the Justice League with Batman, who was raised by Alfred.
Superman and The Penguin. 
Fiona Webb and Tony Gordon
The Eraser and Alicia Baker
Reaganfan78: Superman’s arch enemy is Lex Luthor, who strikes a deal to gain control of Gotham City during No Man’s Land with The Penguin.
Joshua: Fiona Webb was engaged to The Flash, who’s on the Justice League with Batman, whose GCPD contact is Commissioner Gordon, whose son was Tony Gordon.
Sushi-Volcano: The Eraser was an enemy of Batman, who’s on the Justice League with Superman, who went to Smallville High with Alicia Baker.
Granny Goodness and Kite-Man
Death and catwoman
RagdollRebel: Granny Goodness inducted Harley Quinn into the Female Furies, who used to date The Joker, who enlisted Kite-Man in The War of Jokes and Riddles.
HaruTheCatgirl: Death is the sister I’d Dream, who enlisted Batman in Dark Nights: Metal, whose ex-fiancée is Catwoman.
Woozy Winks & Black Racer.
May I have two turns?
Brainiac and Sinestro
djd187: Woozy Winks is the sidekick of Plastic Man, who was in the JLA with Wally West, whose uncle is Barry Allen, who was pursued through time by the Black Racer.
JLWWSM: You can have as many turns as you like, but this is an easy one: in NO JUSTICE, Brainiac enlisted Sinestro into Team Mystery.
'Mazing Man and…the Eradicator.
Vroom: ‘Mazing Man was inspired to fight crime by Batman, who’s in the Justice League with Superman, who was the template for Eradicator.
Marshmallow Pete and…Booster Gold =)
How about The Riddler and Joker.
Vroom: I’m afraid I’m unfamiliar with Marshmallow Pete. If this is a DC character, then you got me. What’s he from?
Reaganfan: The Joker went to war with The Riddler in, well… The War of Jokes and Riddles.
He’s a DC character I created.
HubCityQuestion
Just awesome. I knew that Wally West was the Black Racer at one time, but I never thought there was anyway that u could make a connection to Woozy. Hats off & mask always on to u. Except when Huntress nursed u back to health in JLU after Milo tortured you. I would take my mask ( & anything else she wanted) off for Huntress too.