Although the Orcish army is too large for your forces to battle alone, you may be able to launch a raid against Auchindoun. Should your strike succeed, you would force their army to retreat - or be cut off and destroyed.
Raze the Fortress of Auchindoun and retreat before their forces can rally against you.
Turalyon and Danath must return to the Circle of Power after destroying Bleeding Hollow (Orange)
As the briefing suggests, the easiest way to win this mission is to use all your starting units to immediately attack and destroy the orange player, and then retreat your Heroes back to the Circle of Power. While it is also possible to win in the traditional way, by building a base and wiping out the enemies one by one, this is much harder to achieve in this mission.