By qualifying for the JGP Final, Mroz received a bye to the 2008 U.S. Championships. At Nationals, Mroz competed for the second time on the junior level. He placed 3rd in the short program and 2nd in the free skate to win the silver medal overall, 10.13 points behind champion Rippon. He was subsequently placed on the team to the 2008 World Junior Championships where he placed 3rd in the short program after landing a 3A-3T combination. He placed 5th in the free skate to place 4th overall, placing 3.40 points behind bronze medalist Guan Jinlin.