Although single-atom catalysts (SACs) with transition metal-nitrogen complexes have been studied widely, investigations that use light-element atoms to adjust the coordination environment of the central metal atoms in metal-nitrogen complexes are still rare but show enormous potential for various electrocatalytic reactions. Herein, we design novel SACs based on monolayer BN adjusted by B, C, or O coordinating atoms as catalysts for the CO2 reduction reaction (CRR). These SACs are denoted as M@BN_D (BN = monolayer boron nitride; D = B, C, or O atom; M = Co, Cr, Fe, Mn, Mo, Pd, Pt, Ru, V, W, Ni, Zn, Zr, Ag, Au, Cu, or Ti atom) and are investigated as CRR catalysts using density functional theory calculations. Among these structures, we identified some promising candidate catalysts for CRR with impressive low limiting potential (UL): Pt@BN_C with a UL of -0.18 for the product CH4 and Co@BN_C and Au@BN_O with UL of -0.41 and -0.37 V, respectively, for the product CH3OH. In particular, Pt@BN_C shows a remarkable reduction in UL for the product CH4 compared to any existing catalysts, synthesized or predicted. In addition, the ultralow UL for CRR on Pt@BN_C was derived from the unique bonding feature between the single metal atom and adsorbates and the modulation of ionic interactions induced by the coordination effect of the C atom.