By deploying Phyrexian Revoker and naming Lethal Vapors as it enters the battlefield, you effectively muzzle the enchantment's self-destruction ability so it can never be activated. With its escape hatch permanently sealed, Lethal Vapors sits safely on the battlefield relying on its static trigger to instantly destroy any and all creatures the moment they enter. This creates a ruthless, inescapable lock that completely halts creature-based strategies in their tracks.