Lady of the Silver Castle

Vigilance, Flash
Hexproof and Indestructible by spells and abilities as long as you control an exiled instant card.
Whenever you cast an instant spell, you may search your library for an instant card with lesser converted mana cost, reveal it, and put it into your hand. You may only activate this ability once each turn. This creature costs {1}{w}{b} less to cast if an instant was cast this turn.