I never think of Ed Wood as a crossover-guy, but technically he is, in that he uses one support-character, "Kelton the Cop," in three of his 1950s wonders: BRIDE OF THE MONSTER, PLAN 9 FROM OUTER SPACE, and NIGHT OF THE GHOULS. BRIDE and GHOULS seem more like a standard XO, thanks to the more substantial presence of Tor Johnson's Lobo.
