Costello, 23, has 19 points (11 goals, eight assists) and 69 penalty minutes in 34 games as team captain with Notre Dame this season. He was originally selected by Ottawa with the 146th overall pick in the 2009 NHL Entry Draft.
Mullen, 27, has 20 points (7-13) in 46 games this season with Utica of the American Hockey League.
I'm here to develop a winning culture and a winning team. There is a bright future ahead of this team. A lot of young, great hockey players here and on the way … a fan base that's passionate about the game of hockey.
— Dan Bylsma after being introduced as new coach of the Buffalo Sabres