Cascade is a triggered ability that was introduced in Alara Reborn.   It returned in the Chaos Reigns deck of Planechase 2012.
From the Comprehensive Rules:
- 702.84. Cascade
- 702.84a Cascade is a triggered ability that functions only while the spell with cascade is on the stack. Cascade means "When you cast this spell, exile cards from the top of your library until you exile a nonland card whose converted mana cost is less than this spell‘s converted mana cost. You may cast that card without paying its mana cost. Then put all cards exiled this way that weren‘t cast on the bottom of your library in a random order."
- 702.84b If a spell has multiple instances of cascade, each triggers separately.
- Cascade triggers when the spell that has it is cast, not when it resolves (that is, before the permanent would enter the battlefield).
- Here's the timing for cascade:
- 1) You cast a spell with cascade.
- 2) The cascade ability triggers and goes on the stack on top of the original spell.
- 3) The cascade ability resolves. If you find an applicable card that you'd like to cast, you do so.
- 4) The spell you cast as a result of the cascade ability resolves.
- 5) The original spell resolves.
- For the most part, cascade is mandatory. You must exile cards from the top of your library, even if you know that you won't exile anything you want to cast. Whether or not you cast the last card you exile is the only optional part.
- The spell you cast as a result of the cascade ability resolves before the original spell. If you cast a creature spell with cascade and then cast an Aura as the result of the cascade ability, you can't enchant that creature with it because the creature spell hasn't resolved yet.
- Cascade won't trigger if you put a copy of a spell with cascade on the stack (due to Cloven Casting or Twincast, for example). That's because you didn't cast the copy (such as with Isochron Scepter).
- Countering the original spell doesn't counter the cascade ability.
- Since cascade is a triggered ability, anything that interacts with a triggered ability (such as Stifle) will interact with cascade.
- All players can see the cards you exile as the cascade ability resolves.
- If you exile a split card this way, check if at least one half of that split card has a converted mana cost that's less than the converted mana cost of the spell with cascade. If so, you can cast either half of that split card.
- If you cast a card this way, you cast it as part of the resolution of the cascade ability. Timing restrictions based on the card's type (such as creature or sorcery) are ignored. Other restrictions are not (such as "Cast [this card] only before attackers are declared").
- A spell cast as part of the resolution of cascade is cast from exile, not from your library. Abilities that prohibit you from casting cards from your library (such as Grafdigger's Cage's second ability) will not stop you from casting a card with the cascade ability.
- If you cast a card "without paying its mana cost," you can't pay any alternative costs, such as evoke or the alternative cost provided by the morph ability. If it has X in its mana cost, X must be 0. However, you can pay optional additional costs, such as conspire, and you must still pay mandatory additional costs.
- A card cast with cascade behaves like any other spell. It can be countered. If you cast another card with cascade this way, the new spell's cascade ability will trigger, and you'll repeat the process for the new spell.
- Casting a card with the cascade ability is optional. If you choose not to, the card is put on the bottom of your library in a random order along with the other cards exiled with cascade.
- If you cast a spell with cascade and there are no nonland cards in your library with a converted mana cost that's less that that spell's converted mana cost, you'll exile your entire library. Then you'll randomly rearrange those cards and put them back as your library. Although you're essentially shuffling those cards, you're not technically doing so; abilities that trigger whenever you shuffle your library won't trigger.
- Enlisted Wurm -
Creature — Wurm
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
 Color percentages
There are a total of 15 cards that involve cascade, which divide by color as such:
 Enchantment that grants Cascade
 External links