Why couldn’t Ashwathama unleash his powers

Why couldn’t Ashwathama unleash his powers of being Shiv Ansh and be the second Shiva on the Kurukshetra War and make Kauravas win the battle? Ashwatthama has no special powers which he could unleash and make Kauravas win the war. Also, technically he was not the ansh of Lord Shiva. He was born of the combined ansh of Lord Shiva, Yama, Kama and Krodh. The only special thing he has was a gem in his forehead which kept him free from hunger, thirst, sleep, fatigue and disease. It also protected him from death by beings lower than human beings.