Sandra Dimir agent

Whenever a creature enters the battle field, Surveil. Sandra gets +x/+x until end of turn, where X is the creatures mana cost.
{u/b}{u/b}draw two cards, then discard a card.
{p/b}{p/b}{p/u}{p/u}you may cast a spell from your grave yard without paying its mana cost, then exile the card.