The Gateway Arch is a 630 foot monument on the west bank of the Mississippi River reputed as the world's tallest arch and "Gateway to the West."
Hedylogos manifested above the Gateway Arch and created a legion of Compliment Sprites that infested the general vicinity. Hedylogos' induced a feeling comparable to intoxication from alcohol and enthralled people within its zone of influence. Anything suggested by the sprites, good or bad, would be immediately attempted by the thralls.
On September 14, the Ghostbusters confronted Hedylogos. Lou Kamaka lured the thralls away in a police cruiser she commandeered. Special Agent Melanie Ortiz, Egon Spengler, and Janine Melnitz doused Hedylogos in negatively charged Psychomagnotheric Slime to weaken its influence and P.K.E. then trapped it. Egon collected ectoplasm left behind by the entity at the Arch and planned to test a theory that Hedylogos' power was similar in nature to pheromones.