Trinisphere is a rare Artifact card from Secret Lair Drop (SLD), collector number 2838. Current market price: $49.99, TCGplayer market prices via Scryfall.
As long as this artifact is untapped, each spell that would cost less than three mana to cast costs three mana to cast. (Additional mana in the cost may be paid with any color of mana or colorless mana. For example, a spell that would cost {1}{B} to cast costs {2}{B} to cast instead.)