Agatha's Soul Cauldron is a mythic Legendary Artifact card from Wilds of Eldraine Promos (PWOE), collector number 242s. Current market price: — (foil $56.48), TCGplayer market prices via Scryfall.
You may spend mana as though it were mana of any color to activate abilities of creatures you control. Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron. {T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.