Mumford and Sons have been on tour this summer and they've been having a band called Gang of Youths open up for them. Unfortunately, their openers had to cancel because of illness.
They were short on time, so they decided they'd do something special for their fans in Phoenix. The band dressed up in costumes and took the stage, playing a bunch of covers.
The band also posted a couple cryptic messages on their twitter account:
pretty epic move from a great band!