Atara, Martyr of the Light

{t}: Sacrifice Atara, Martyr of the Light.
Whenever a White or Black creature dies, you
may return Atara to the battlefield under your
control.
If Atara dies, you may pay {x}{w/b} and return target nonland permanent with converted mana cost X.
A queen with an unforgivable sin, doomed to return
to her past and to witness it again and again.