Titans' Nest (Promo Pack) [Ikoria: Lair of Behemoths Promos]

At the beginning of your upkeep, look at the top card of your library. You may put that card into your graveyard.
Exile a card from your graveyard: Add {C}. Spend this mana only to cast a spell that's one or more colors without {X} in its mana cost.