User blog comment:Allgorhythm/Subduing Ur-Dragon Generation 722/@comment-24458380-20150516194214/@comment-23878607-20150517065745

Also note that the two pawns don't have perfect control of the Ur's movement patterns; they lose control of its stagger state when their str/mag boosters wear off. If I'd kept those up without a lapse, then the Ur would not have spun around, nor would it have been able to lift off in that backwards leap towards the clip's end.

That is the Arisen's job, to make sure that the Ur's stagger state is unbroken. ;)  This can be easily done with a Blast Arrow shot or dagger-striking the Ur's hearts hard enough. For a Sorcerer, High Maelstrom does it, and so does HFB in certain circumstances.