In the summer of 2008, Mangan signed for Forest Green Rovers in the Conference Premier. It was at Forest Green that Mangan's goalscoring reputation began to form; his first season saw him finish as the league's top scorer with 26 goals in 41 games.
In 2008, Mangan signed with Forest Green Rovers in the Conference Premier. His goal-scoring prowess began to emerge at Forest Green; his first season saw him top the league's scoring charts with 26 goals in 41 games.