The background of Narcosis is unknown. He holds a grudge against Gotham City, blaming it for the abuses of its foster care system.
He uses gas grenades to spread his "dream gas", a combination of Ketamine and Acetylcholine. Ketamine sedates his victims, prevents them from feeling pain, and causes hallucinations. Acetylcholine affects the nervous system and increases sensitivity to external stimulation. His victims experience paralysis and hallucination.
In his initial appearance "Batman: Shadow of the Bat" #50 (May, 1996), Narcosis used his dream gas on Batman. The victim hallucinated about facing an army of old foes. Narcosis easily escaped his foe. In #51 (June, 1996) Narcosis took over a dairy factory. He wanted to contaminate the milk supply of Gotham City. Aiming to trap the residents of the city in an unwaking, lucid dream. Meanwhile Batman was still drugged. In #52 (July, 1996), Batman and Robin (Timothy Drake) managed to track down Narcosis. Robin managed to stop the delivery of the contaminated milk, while Batman faced Narcosis in combat. The battle ended when Nemesis fell into a vat full of contaminated milk. Getting trapped in an unwaking dream of his own.
Narcosis resurfaced in #78 (September, 1998). With Gotham City suffering from the after-effects of a major earthquake, Narcosis was convinced that he could provide salvation to its citizens. In #79 (October, 1998), Narcosis entered an ill-advised alliance with the Mad Hatter. His "ally" betrayed him, claiming the uniform and equipment of Narcosis for himself. The body of Nemesis, unconscious, supposedly fell victim to a fire. His death is not fully confirmed.