Titans' Nest is a rare Enchantment card from Ikoria: Lair of Behemoths (IKO), collector number 212. Current market price: $0.33 (foil $0.43), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, surveil 1. (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.