The Paradox Heart

Instant and sorcery spells you cast cost {1}
less to cast.
Whenever you cast or copy an instant or sorcery
spell, randomly select a player and exile the top
X cards of that player's library, where X is
the spell's mana value. Randomly select one of
those cards, and return the rest to the bottom of
their owner's library in a random order. You cast
the selected card without paying its mana cost.
Partner with Rhanva, the Shattered