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've got a lot of experience and there's a lot of young guys. It's even making me excited a little more. It's kind of a new life. At my age, I feel like I know a lot of things what to do, but I just cannot do it anymore. It's a lot easier to tell them what to do because they've still got the legs and hands to do it. I just know things, but I cannot do them anymore.
— Jaromir Jagr after making his Panthers debut in a win against the Sabres on Saturday