So this effectively reduces the cost of cards and skills by however many Feathergraces are on your field (except that you still need the full amount of quanta to cast it, kind of like Supernova)?
If so, then this is completely broken with Rustler. You may want to mention that Rustler will only be able to use its skill once if this card is in play.
Other than that, it's quite cute and useful, although you may want to not let it stack. I like (now make a non-Air card!).