Purebred Sliver

Each Sliver creature card in your graveyard has progress. The progress cost is equal to the card's converted mana cost. (Pay a card's progress cost and exile it from your graveyard: Search your library for a card that shares a creature type with it, reveal it, put it into your hand, then shuffle your library.)
"Some slivers were left behind in the great surging of their evolution, having found environments tha