 In addition to the three prequel mini @-@ episodes , the cast also filmed an additional promotional video , " Songtaran Carols , " which the BBC uploaded during the days leading up to the broadcast . The video featured Starkey singing modified versions of several Christmas songs in character as Strax as his castmates look on , before everyone breaks character and begins laughing . 
 In addition to the three prequel mini @-@ episodes , the cast also<a href='been_done' title='1'><mark></mark></a> filmed an additional promotional video , " Songtaran Carols , " which the BBC uploaded during the days leading up to the broadcast . The video featured Starkey singing modified versions of several Christmas songs in character as Strax as his castmates look on , before everyone <a href='uninflect' title='2'><mark>breaks</mark></a> character and <a href='uninflect' title='3'><mark>begins</mark></a> laughing . 
In addition to the three prequel mini @-@ episodes , the cast also done filmed an additional promotional video , " Songtaran Carols , " which the BBC uploaded during the days leading up to the broadcast . da video featured Starkey singing modified versions of several Christmas songs in character as Strax as his castmates look on , b4 everyone break character and begin laughing .