Definitely Deadman, Constantine, Sandman and The Spectre! The MUST READ would be Alan Moore’s run on Swamp Thing (can’t wait for the show).
Constantine.
Swamp Thing, Etrigan, The Spectre
Phantom Stranger tops my list (although I suppose it’s debatable if he is horror or more accurately, suspense.
Deadman is another. Boston can be utilized so well and make such great choices with his power. But, when he screws up, he can really screw up. Case in point, taking over Bats and using a gun to kill somebody. If Z or Constantine would have been around to give Deadman a physical form, Bats would have kicked his butt into the next century.
The specter Constantine swamp thing the demon
The specter Constantine swamp thing the demon
Batman vs the Mad Monk. The Matt Wagner Story was part pulp novel and part horror just done so beautifully well. But also in his own right the Joker is certainly a horror character, or Two Face and Scarecrow.
Dr 13, Phantom stranger
Phantom Stranger, Deadman, Constantine and Spectre
Etrigan and the Phantom Stranger
Len Wein and Bernie Wrightson. And Len Wein and Jim Aparo.
Victor Zsasz
Batman: Shadow of the bar and Knightfall and Gotham. A serial killer. He loves killing women. Carves a mark on himself for each victim. Uses runaway children to fight to the death while people make bets. A truly horrifying hero.
I’ve always like the Spectre, also i think would be a great horror film.
Boston Brand aka Deadman
Elvira in DC’s House of Mystery
Anything with Constantine.