The Mysterious Sphere is a rare Legendary Artifact card from Unknown Event (UNK), collector number RA05. Current market price: $9.79, TCGplayer market prices via Scryfall.
Advertising — {T}: Exile the top card of your library. You gain 1 life. Show — At the beginning of combat on your turn, if there are three or more cards exiled with The Mysterious Sphere, you may put them into your graveyard. If you do, create copies of each nonland card among them. You may cast the copies without paying their mana costs. If you cast a creature spell this way, it gains haste and "Sacrifice this creature at the beginning of your end step."