Hall of Chaotic Invocation

At the beginning of your upkeep, exile the top card of your library, then choose one:

• You may play the exiled card until the end of turn.

• Until the end of turn, the cost of each spell you cast is reduced by the number and type of mana symbols in the exiled card's cost. This cannot reduce the cost of the spell to less than 0. (For example, if the mana cost of the exiled card is {3}{u}{u}{r}, spells you cast this turn would be reduced by
{u}{u}{r}. This cannot be used to decrease ge