Magnetohydrodynamics (MHD), Casson nanofluids, mixed convection, and thermal radiation are crucial in enhancing heat transfer efficiency and system performance in engineering and industry, particularly in heat exchangers and combustion systems, thereby driving technological progress and economic growth. The primary objective of this study is to explore the mixed convective heat and mass transfer in the boundary layer of Casson nanofluid flow. This flow passes through an upright dish and is subjected to an externally applied magnetic field and thermal radiation. To analyze this, suitable non-dimensional variables transform the time-dependent governing equations. The dimensionless equations are numerically solved using the explicit finite difference method. The solution convergence is ensured properly by thoroughly checking comprehensive stability and convergence criteria. This research provides detailed profiles that showcase the velocity, temperature, concentration, and isothermal distribution, along with patterns of streamlines and unique features of various flow, thermal, and concentration fields. Through a linear evaluation of the radiative heat flux, it is convincingly shown that the Lorentz force significantly influences flow profiles, ultimately leading to their reduction. The numerical results indicate that the velocity significantly increases by approximately 70.56% in the free convection area. There is a substantial increase in friction by 17.89%, demonstrating excellent flow resistance. The thermal performance also improves, showing an approximate enhancement of 12.98%, suggesting a higher heat transfer efficiency. Three new linear regression equations for multiple variables are derived. It explores the use of thermal radiation in Casson nanofluid flow over a flat plate affected by MHD, resulting in enhanced heat transfer and improved flat plate cooling.