Another unusual choice would have been Walt Simonson.
Simonson did a few scattered mystery stories for WEIRD WAR 10, WEB OF HORROR 1, a few issues of SAVAGE SWORD OF CONAN, SWORD OF SORCERY 4, and closest to SWAMP THING, a visually striking revival of Doctor Fate in
FIRST ISSUE SPECIAL 9, Dec 1975.
Years later, Simonson also did a nice treatment of Stephen King's "The Lawnmower Man" in BIZARRE ADVENTURES 29, in 1981.
Coming off his award-winning run on the Manhunter series in DETECTIVE COMICS 437-443 in 1973-1974, SWAMP THING would have been another high-profile series for Simonson, and a really interesting artistic pick.
