Complex sentence: Sean Monahan scored his 20th goal of the season in the loss, becoming the first Flames rookie since Dion Phaneuf in 2005--06 and first rookie forward since Jarome Iginla in 1996--97, to reach the mark.
Split into simpler sentences: Sean Monahan scored his 20th goal of the season in the loss. He became the first Flames rookie since Dion Phaneuf in 2005--06, and first rookie forward since Jarome Iginla in 1996--97 to reach the mark.