Free spells are strong. Let's talk about Cascade.

One important note: this article assumes you understand how the stack works, how priority is passed, and what a triggered ability is.

What is Cascade?

Cascade is a triggered ability on spells. It debuted in Alara Reborn, only on multicolored cards, and has since been in several supplemental sets and various Commander precons.

When you cast a spell with Cascade, you Exile cards from the top of your Library until you Exile a nonland card whose Mana Value is lower than that of the spell with Cascade. You may cast that spell without paying its mana cost.

That seems simple.

It actually kind of isn't. The timing of all this becomes important. There are also a ton of specific rules quirks with this, but let's start with timing, using a relatively simple example.

1. You cast Bloodbraid Elf. Bloodbraid Elf goes on the stack.
2. Cascade triggers. The Cascade trigger goes on the stack on top of Bloodbraid Elf.
3. Priority passes. No one responds.
4. Cascade resolves. You flip over two Forests and a Mountain, then a Lightning Bolt.
5. You decide you want to cast the Lightning Bolt without paying its mana cost.
6. Lightning Bolt is cast and goes on the stack. Again priority passes but no one responds.
7. Lightning Bolt resolves. You choose targets and deal three damage somewhere.
8. The two Forests and the Mountain get put in a random order and put on the bottom of your Library.
9. Bloodbraid Elf resolves, hitting the Battlefield.

Why is this level of specificity required? Several reasons.

First, you can't target the spell with Cascade with a spell you Cascade into, because the spell with Cascade hasn't resolved yet. In other words, you can't target your own Bloodbraid Elf with that free Lightning Bolt. It's unlikely you might want to do that, but if you Cascade into Blanchwood Armor instead of Lightning Bolt, you can't stick the Armor on the Elf.

Second, various things can be responded to by the table, but they are specific and individual and not necessarily intuitive. When priority first passes, the Bloodbraid Elf can be countered (with, say, Counterspell), but the Cascade trigger will still go on the stack, and the Lightning Bolt will still be cast (countering the spell with Cascade doesn't counter the spell you Cascaded into). Additionally, the table could counter the Lightning Bolt but you'd still get your Elf. Or someone could Stifle the Cascade trigger, but you'd still get your Elf (and have three Lands on top of your Library, because they wouldn't ever be revealed as part of the Cascade or get put back on the bottom in a random order).

Okay, I think I got it.

It gets more complicated.

Each instance of Cascade happens individually, and they must be approached in that way. Let's complicate our example. So it doesn't have 40 steps, I'm going to combine some.

1. You cast Enlisted Wurm. It goes on the stack, as does its Cascade trigger. No one responds.
2. You flip over a Forest, a Plains, and a Mountain, then a Bloodbraid Elf. You opt to cast the Elf without paying its Mana cost, so you do. The Elf goes on the stack. You put the three Lands in a random order and put them on the bottom of your Library. The Elf's Cascade trigger goes on the stack.
3. You flip over two more Lands, then Lightning Bolt. You opt to cast it without paying its mana cost.
4. Lightning Bolt goes on the stack. The two Lands get randomized and put on the bottom of your Library.
5. Lightning Bolt resolves, shooting something for three.
6. Bloodbraid Elf resolves, hitting the Battlefield.
7. Enlisted Wurm resolves, hitting the Battlefield.

This functions the same way if a spell has multiple instances of Cascade (like Maelstrom Wanderer), except each instance goes on the stack right at the beginning, then each one resolves in order and in full. (You randomize all Exiled cards not cast and put them on the bottom of your Library in between each instance of Cascade.) If you already have two instances of Cascade on the stack, and the first one resolves into a new Cascade, the new Cascade trigger goes on the stack on top, which means it will resolve first.

Huh?

Fair. New example!

1) You cast Maelstrom Wanderer. The Wanderer goes on the stack, followed by two instances of Cascade, where our target Mana Value is <8 (the Mana Value of Maelstrom Wanderer).

2) You resolve the first Cascade trigger and flip into Bloodbraid Elf, which you cast. It goes on the stack, on top of Maelstrom Wanderer's second Cascade trigger. So the stack looks like this:

a. Elf Cascade target value <4

b. Elf

c. Wanderer Cascade target value <8

d. Wanderer

3) We resolve last in, first out, so now the Elf's Cascade trigger happens. We have to flip by that Myr Battlesphere and instead go to the Lightning Bolt. The Bolt goes on the stack, the Battlesphere gets randomized and sent to the bottom, and the Bolt resolves.

4) Then the Elf resolves, then the final Maelstrom Wanderer trigger, then finally Wanderer itself.

If you don't keep careful track of how your triggers line up, you can end up casting a spell for free you shouldn't cast - in the above example in a casual game, it would be very easy to think the Battlesphere could be cast because you forgot who's Cascade trigger it was.

Sheesh. Anything else?

Unfortunately, yes.

Cascade is, almost always, mandatory. You have to Exile cards from the top of your Library until you either hit a legal target (a nonland spell with Mana Value less than the initial spell with Cascade) or you Exile your entire Library. The only choice you get in the matter is whether or not you cast the spell you flip over - you don't have to.

In the case of a spell with multiple modes, thanks to a rules update in 2021, the mode you're using has to have a Mana Value less than the spell with Cascade. So if you flip into Breaking // Entering with Bloodbraid Elf, you can cast Breaking but you can't cast Entering.

Cascade is a cast trigger, not an Enters trigger. So if you Clone something with Cascade, Cascade won't trigger. You have to cast the spell. Likewise, if you "cast without paying its mana cost", you'll get the Cascade trigger, but if you "put it on the Battlefield without paying its mana cost", you won't.

Everyone gets to see what you flip over as you resolve Cascade.

Timing restrictions due to a card's type (like Sorcery or Artifact) are ignored when resolving Cascade. In other words, if you cast Bloodbraid Elf with Flash during your opponent's End Step and flip into an Ichor Wellspring, you can cast the Ichor Wellspring (though you'll draw the card off the Wellspring's Enters effect before the Elf resolves!).

Other timing restrictions ("cast this spell only during your Combat phase before Attackers are declared," for example) are not ignored. If you flip a card over with a restriction like that, you can't legally cast it and your Cascade will fizzle.

No alternative costs. You can't cast an Evoke cost instead of the actual mana cost. You can't put a Morph card down upside down. Most importantly, X = 0 and you can't increase it with X in the mana cost.

Yes additional costs, though. You can Conspire or Entwine, pay a Kicker cost or Forage, to get the extra effect. And you are required to pay mandatory additional costs, like the Sacrifice on Village Rites.

Two more things about putting cards back after a Cascade trigger.

First, you are Exiling the cards as you flip past them. So while you'll very likely physically shuffle the cards together to randomize them, you're not actually shuffling them. This is important because...

Second, if you don't have a legal target in your Library when you cast a spell with Cascade, you will Exile your entire Library, randomize it, and put it back. While you have physically shuffled, you didn't from the game's perspective, so anything that triggers or happens because you shuffled your Library will not happen in this instance.

Thanks a lot, dude. This is ridiculous

You're not wrong. It is, and it's more complicated than it looks on its face.

It's also very powerful, and with thoughtful deck building you can really wrench a lot out of Cascade. Remember your timing and restrictions and minimize situations where things won't work how you need them to.

I find a visual aid helpful when doing complicated Cascade stuff (which happens, because I play a Maelstrom Wanderer Commander deck quite a bit). I use dry-erase token cards and physically build a stack, resolving one by one and setting cards aside or adding them as the various triggers resolve. Each dry-erase card is one item on the stack, so they say things like "Maelstrom Wanderer Cascade Trigger" or "Lightning Bolt Resolves". Everyone at my table likes it because it keeps everything clear, fair, and understandable.

Now get out there and flip over some powerful cards!

Thanks for reading.