December 2015 was a very turbulent month for the Pittsburgh Penguins, who fired their coach and were ravaged by injuries and the end of a career. Mike Johnston was removed from his post as head coach after a Dec 11 shootout loss to LA, after going 2-2-1 in the 5 games he coached in the month, with the team meandering through a difficult season.
His replacement, Mike Sullivan, dropped the first 4 games he coached but has the team's metrics a lot stronger and Pittsburgh ended the month of December with a 3-1-1 record.
In between all of that, the Pens swung just the second trade in the whole league this season, to rid themselves of Rob Scuderi, sadly saw the end of Pascal Dupuis' playing career, dealt with meaningful injuries to their franchise goalie and #1 defenseman.