In our last game I made a desperate move against Moria with Lorien's elves. Two elves besieged a lone Sauron orc. Then I got two Ent Event Cards put two of my four Ents into Parth Celebrant and Dimrill Dale and attacked the lone orc with the third. This way I won the siege.
Letting the Ents march on Moria seems strange - but it is legal, isn't it?