This study investigates the performance and emission characteristics of a dual-fuel engine running at full load on diesel, biodiesel blends (B5 and B20), hydrogen-oxygen (HHO) gas, and a blended additive (combination of acetone, ethanol, sulcatol, and dimethyl carbonate). Tests were conducted to evaluate key performance metrics, including brake power, brake-specific fuel consumption, and various emissions, including unburned hydrocarbons, carbon monoxide, carbon dioxide, and nitrogen oxides. The results show that if the effects of HHO and the blended additive are excluded, diesel consistently outperforms both biodiesel blends (B5 and B20) regarding braking power and efficiency and exhibits superior combustion properties. However, the addition of HHO improved the brake power and reduced the emission of unburned hydrocarbons and carbon monoxide in biodiesel blends, especially at lower concentrations of the combined additives. However, while CO2 emission was lower for biodiesel blends than diesel, the presence of HHO also improved NOx emissions. These findings demonstrate the potential of HHO as a performance enhancer in biodiesel applications while emphasizing the need for careful management of NOx emissions. Also, the effect of the combined additives in certain conditions, such as the emission of unburned hydrocarbons or the emission of nitrogen oxides in high percentages of using biodiesel (B20A6), is more prominent, which can improve the conditions in critical conditions. However, the B5A2 fuel sample can be relatively identified as a suitable fuel in different percentages of HHO from the point of view of engine emissions.