Two-dimensional boron-nitrogen-carbon heterostructures with variable composition and interaction strength were obtained by one-step one-precursor synthetic route based on dimethylamine borane pyrolysis by changing the metallic surfaces and the temperature of growth. Hybrid single layers composed mainly of hexagonal boron nitride and graphene domains (h-BNG) with different relative concentration and surface hybridization were grown on polycrystalline metallic foils including Pt and earth abundant metals such as Ni and Fe. An almost freestanding layer of h-BNG grown on Pt was successfully transferred on a SiO2/Si substrate by a simple electrolytic delamination. The atmospheric gas intercalation between h-BNG and Pt of the sample stored in air before the transfer procedure was demonstrated to be effective for a facile h-BNG detachment from the metal during the delamination bubbling process. This facile and flexible synthesis and transfer route opens up the way to applications of hybrid B-N-C monolayer in technology, catalysis and 2D confined chemistry, gas-sensing and hydrogen storage.