Complex sentence: He made his NHL debut on December 18, against the Washington Capitals at Washington and three night later scored his first NHL Point (assist) on December 21 against the Boston Bruins, at St. Louis.
Split into simpler sentences: He made his NHL debut on December 18, against the Washington Capitals at Washington. He scored his first NHL Point (assist) on December 21 against the Boston Bruins, at St. Louis.