Jeleva, Nephalia's Scourge

Flying
When Jeleva enters, 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 spell from among cards exiled with Jeleva without paying its mana cost.

Commander 2013 Oversized

Commander 2013

Flying
When Jeleva, Nephalia's Scourge enters the battlefield, each player exiles the top X cards of his or her 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.

If Jeleva leaves the battlefield, the exiled cards will remain exiled indefinitely. If Jeleva enters the battlefield again, it won't be associated with the cards the "other" Jeleva exiled. The new Jeleva will exile a new set of cards. Only those cards can be cast using Jeleva's last ability.

If the card has {X} in its mana cost, you must choose 0 as its value.

If you cast a card "without paying its mana cost," you can't pay alternative costs such as overload costs. However, you can pay additional costs such as kicker costs. If the card has mandatory additional costs, you must pay those.

If you cast an instant or sorcery card using Jeleva's last ability, you do so while that ability is resolving. If you choose not to (or you can't), you won't get a chance to cast it later unless the ability triggers again.

The card is cast before blocking creatures are declared.

When casting an instant or sorcery card this way, ignore all timing restrictions based on the card's type. Other timing restrictions, such as "Cast [this spell] only during combat," must be followed.

If Jeleva enters the battlefield without being cast, then no mana was spent to cast it. This means X will be 0, so no cards will be exiled.

The amount of mana you spent to cast this creature is usually equal to its mana value. However, you also include any additional costs you pay, including the cost imposed for casting your commander from the command zone.

You can't choose to pay extra mana to cast a creature spell unless something instructs you to.