Agatha of the Vile Cauldron is a mythic Legendary Creature — Human Warlock card from Wilds of Eldraine (WOE), collector number 199. Current market price: $11.16 (foil $6.86), TCGplayer market prices via Scryfall.
Activated abilities of creatures you control cost {X} less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana. {4}{R}{G}: Other creatures you control get +1/+1 and gain trample and haste until end of turn.