By January 1945, Mostovoy was a machine gunner in the 3rd Battalion of the division's 220th Guards Rifle Regiment. Starting on 14 January, the division began to attack out of the bridgehead. On that day, Mostovoy, despite heavy machine gun and mortar fire from German troops, crept close to the German trenches with his crew and reportedly killed 17 German soldiers, suppressing 3 firing positions. On 25 January, he was one of the first across the Warta and covered the crossing with machine gun fire. During subsequent fighting in the town of Warta, Mostovoy destroyed two German machine guns and reportedly killed 13 German soldiers. He also helped repulse numerous German counterattacks. On 28 February, he was awarded the Medal for Battle Merit for his actions. For his actions, Mostovoy was also awarded the title Hero of the Soviet Union and the Order of Lenin on 24 March 1945. According to Vasily Chuikov, Mostovoy was an extremely big and strong man. During the Oder crossing battle for Hill 81.5, he reportedly attacked German troops with a shovel and his machine gun's mounting after he ran out of grenades and ammunition. Mostovoy also reportedly captured a German soldier by tucking him under his arm. He continued to fight in combat and participated in the Berlin Offensive.