I have been thinking of a flying shield effect for literally the past month or so, ever since the first card idea competition. With all of the new, powerful shield effects, I believe something like this would be just plain overpowered. However, I did come up with one way to make it work. When you fly the shield, it becomes a creature and your shield spot becomes free. The creature version would hold the ability, but the ability would be applied to the shield slot. So basically, a flying shield would "add" its inherent ability to your shield, stacking effects onto one shield. Of course, this is still quite complicated, but at least it's simple to understand.