Ónil, Goddes of the Hearth

Whenever another creature enters the battlefield under your control you can discard
a card. If you do, reveal the first card of your
library, you can play that card until the end
of turn and its mana cost is reduced by {r} for every {1} in the converted mana cost
of the discarded card. Then Onil deals an
amount of damages equal to the difference to
target creature.