Return any number of cards with different converted mana costs from your graveyard to your hand. Put Seasons Past on the bottom of its owner's library.
4/8/2016 The phrase “different converted mana costs” compares the mana costs of cards in your graveyard to one another, not to Seasons Past. You may return a card with a converted mana cost of 6.
4/8/2016 If a card in your graveyard has in its mana cost, X is considered to be 0.
4/8/2016 A card with no mana cost, such as a land, has a converted mana cost of 0.
4/8/2016 You choose which cards to return as Seasons Past resolves, not as you cast it.