[1] At the 2010 IIHF World U18 Championships, Arnold recorded three points in six games as the National Team Development Program, representing the United States, won the gold medal.

[2] At the 2010 National Hockey League (NHL) Entry Draft, Arnold was selected in the fourth round, 108th overall, by the Calgary Flames.

[5] He then capped his season with a national championship as Boston College won its final 19 games, culminating in a 4–1 victory over the Ferris State Bulldogs to win the 2012 Frozen Four tournament.

[7] Following Boston College's 5–4 loss in the 2014 Frozen Four semifinal to the Union Dutchmen, Arnold joined Gaudreau – who was also a Flames draft pick – in signing their first professional contracts.

[9] He made his NHL debut in the Flames final game of the season, a 5–1 loss to the Vancouver Canucks on April 13, 2014.