Power Shifts on Mustang Premium/LE games. These are akin to Walker Bombs on TWD and Back Stage Passes on ACDC. Once earned, they allow you to complete required mode shots, when you wish, by hitting the lockdown bar button (1 free shot per Power Shift).
Many seem to especially rave about Walker Bombs, but few seem to be aware of Power Shifts. Probably due to only having played a Mustang Pro - if a Mustang at all.