Amethyst Core

Sacrifice Amethyst Core: Search your library for
a card and put that card into your hand.
Then shuffle your library.
Whenever you cast a spell from your hand, if it
shares a color with the top card of your graveyard,
you may exile that card. If you do, copy the exiled
card. You may cast that copy without paying its
mana cost.
A unique relic of ethereal essence.