Theyre very valuable even if you dont use them in your decks, and often useful in another format
Every dragon you play brings another devastating ability to the table: removal, lifegain, ramp, or direct damage
Another clever ability that mirrors the game characters function is Yuna, Hope of Spira from Final Fantasy X
The key to doing this kind of card would be making it feel like a I lit your stuff on fire, drop it kind of feel rather than a white taxing effect
In this case, the value is largely from the fact that it's the prerelease foil version of the card , which is stamped with the release year in the lower left corner of the card art
In a Blue deck, the Mirari is so (comparatively) weak its not funny