Smoldering Stagecoach

"Cascade" means "When you cast this spell, exile cards from the top of your library until you exile a nonland card whose mana value is less than this spell's mana value. You may cast that card without paying its mana cost if the resulting spell's mana value is less than this spell's mana value. Then put all cards exiled this way that weren't cast on the bottom of your library in a random order."

If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the spell has any mandatory additional costs, you must pay those to cast the card.

Cascade triggers when you cast the spell, meaning that it resolves before that spell. If you end up casting the exiled card, it will go on the stack above the spell with cascade.

The mana value of a split card is determined by the combined mana cost of its two halves. If cascade allows you to cast a split card, you may cast either half but not both halves.

You exile the cards face up. All players will be able to see them.

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