Fir, Knight of the Scales

Vigilance
When Fir, Knight of the Scales attacks, you may
exile a non creature spell from your hand. If you do,
Fir gains +X/+0 until the end of the turn,where X
is the spells mana value.
{b}{b}{b}{b}{b} Exile Fir and return her to the battlefield transformed, tapped and attacking.
Activate only during declare attackers step.