This card is fantastic and a must-have for Eagle decks. It's effect can be used at any time, stacked up multiple copies on the same hero and used for attack or defense depending on the need. With a single Winged Guardian and even two copies of this card you can be defending at +8, likewise with the 1 cost Vassal you can be up to +6 attack. The best ally is Eagles of the Misty Mountains but is a pricey combo.
On a multiple readying action hero like Boromir or Elladan it works best. But also great on Legolas with any combination of Rohan Warhorse, Great Yew Bow, Hands upon the Bow and/or Quick Strike to destroy enemies with arrow attacks from the air. Lastly combos great with Hour of Wrath to turn any hero into Boromir.