Serenity

When Serenity enters, look at the top 6 cards of your library. Exile a nonland card from among them and put the rest on the bottom of your library in any order. Spells you cast that share a card type with the exiled card cost {1} less to cast. Whenever you cast a spell that shares a card type with the exiled card, put
a calm counter on Serenity.

Sacrifice Serenity: You may cast the exiled card until end of turn by paying its mana cost reduced by {1} for each calm counter on Serenity.