Phthisis is a uncommon Sorcery card from Time Spiral (TSP), collector number 122. Current market price: $0.20 (foil $0.69), TCGplayer market prices via Scryfall.
Destroy target creature. Its controller loses life equal to its power plus its toughness. Suspend 5—{1}{B} (Rather than cast this card from your hand, you may pay {1}{B} and exile it with five time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)