Private First Class Mryncza was a member of Company E, 2nd Battalion, 7th Marines, 1st Marine Division. He was listed as Missing in Action while fighting the enemy at the Chosin Reservoir, North Korea on 27 November 1950. He was presumed dead on 22 October 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Mryncza was awarded the Purple Heart, the Prisoner of War Medal, the Combat Action Ribbon, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal and the Korean War Service Medal.