When activating her Ultimate, mercy will do a EMP that cleanses friendly players, phases them out, and heals them for 50.
Was supposed to be like suzu, but due to workshop limitations it will not cleanse every effect (e.g. not discord)
After 3 seconds valk will be cancelled by swapping to a different hero and back instantly. I don't think there is a more elegant way to shorten ult duration for mercy specifically, so this will have to do.