Jeleva, Nephalia's Scourge

Jeleva, Nephalia's Scourge {1}{U}{B}{R}

Legendary Creature - Vampire Wizard | Power/Toughness: 1 / 3
Flying
When Jeleva, Nephalia's Scourge enters the battlefield, each player exiles the top X cards of their library, where X is the amount of mana spent to cast Jeleva.
Whenever Jeleva attacks, you may cast an instant or sorcery card exiled with it without paying its mana cost.