Monstrous Vortex

Some spells and abilities that cause you to discover may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won't resolve and you won't discover.

If you can't cast the discovered card (perhaps because there are no legal targets for the spell), you'll put it into your hand.

When you discover, you must exile cards. The only optional part of the ability is whether you cast the exiled card or put it into your hand.

If the discovered card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

The mana value of a split card is determined by the combined mana cost of its two halves. If discover allows you to cast a split card, you may cast either half (as long as its mana value is less than or equal to the effect's discover value) but not both halves.