This one is very easy. Simply find someone who is playing as Reaper, Pharah, McCree, Genji, Roadhog, Bastion, or Torbjorn and wait for them to use their ultimate. Aim carefully and it will pop. I found Pharah and Roadhog to be the easiest as one is stationary and the other moves slowly. I can't confirm if Winston or Zenyatta will work because I have heard that they can continue if they are awakened.