Watch the Skies - Kill 50 Uruks with Strike From Above.
For a quick way to get this challenge, head to any stronghold, begin fighting some Uruk's until one of them raises the alarm...giving you more Uruk's to Strike From Above. Find a building where the Uruk's cannot follow you on top of, kill any surrounding archers, then begin with the strikes from above. To do this quickly, you must have just about all of the Uruk's indicators on yellow showing that they have lost you, when your last known position ghost appears. Once a large part of the group has the yellow indicator rather than red indicator, move to the edge in stealth holding
watching your lower right hand corner for the stealth kill
option to appear. As soon as you get stealth kill with
as this will not kill them and you will have to climb more times then needed.
Otherwise, if you run out of Uruk's just find another group of them in the stronghold, they tend to respawn in groups of about ten, so stick close to the entrance or wherever you entered.
This challenge is straightforward and simple, just giving a quick way to obtain for those who seek help. Message me for any other tips. Good luck!