And here's the returning mechanic for the set.

You don't need a returning mechanic per set. It's usually one per block. Cascade seems like a really strange choice, too.

How does cascade tie into LotR?

It fits the idea of little actions triggering big events, i.e. Boromir throwing a stone into the lake awakes the Watcher in the Water and Pippin dropping something into a well alerts the Orcs to the company's presence.

Also, Morph, Delve, and Rebound were all returning.

Odd, since Cascade technically is big events spill into smaller events. I suppose that's fine. I do wonder, however, if there's a reasonable way to make a 'reverse cascade'. Obviously, not by doing the obvious thing. :p

Maybe by paying some sort of 'Reverse Cascade' cost? I hear that 60% of all Magic keywords are just something pretending not to be kicker...

How about, "When you cast ~, reveal the top card of your library. If it's a nonland card with CMC greater than ~'s, you may cast it without paying its mana cost. Otherwise, put it on the bottom of your library." I'm trying to think of a name for that, something along the lines of "Awaken"... but that's already a mechanic.

"Ripple"? Nope, that's also already a mechanic.

Ooh, I could call it Delve to fit with the flavor of the Dwarves awakening something in deep caves under the mountains! Oh wait...

How about Repercussion?

Seems pretty broken, depending on how you cost it.

For flavor, maybe reveal the bottom card of library... I'll have to think about balance.

Repercussion is now in the mechanics page, codename "Uncascade."

Seems terrifying with Scry.

True... which is also a theme in this set. Editing to "When you cast ~, shuffle your library, then..."

Edited mechanic now in mechanics page.

You're not going to have room for flavor text on your repercussion cards, though.

Do you think it's okay to forgo reminder text on more cards than normal for the sake of flavor text in a custom set?

No.

But it's ultimately up to you, and how playable and "realistic" you want the set to be.

I will put reminder text on all Repercussion commons, some uncommons, and forgo it on any rare or mythic that has fitting flavor text, following the idea that NWO mainly affects commons as they are the cards newer players see most, and that higher rarities can require more comprehension of the game sometimes.

I'd add another vote for reminder text on commons.

Reminder text doesn't have to be perfect rules text, mind you - so you could shorten to something like:

When you cast this: cast the bottom card of your library if it costs more, otherwise destroy it.

Having the shuffle also makes me think it would be better as top card; but I presume you have a clever reason for that. I'd omit the shuffle if at all possible though.

Shuffle is just a way to avoid the easy "I scry my mythic 10-drop to the bottom/top of the library, then repercussion it" combos. Which definitely need to be avoided.

This version is still unfortunately massively high variance. It'll feel like the jackpot when you hit, but the opponent will feel really frustrated.

I would like repercussion better if it was like cascade that looked for a card that cost 1 more. Note that I would like it even better if it didn't look for things that cost more.

How would you design to fit the flavor that I wrote about above (small actions triggering major plot points)

Hmm. Maybe an ability word? Repercussion — When you cast this, reveal the top card of your library. If it costs more than ~, [bonus]?"

Or how about "When you cast a spell that costs more than ~, [bonus]"? I guess that stops the creatures being virtual vanilla, though, which increases board complexity.

How about getting the bigger card as a replacement? "When you cast ~, reveal cards from the top of your library until you reveal a card with CMC 1 greater than ~'s. You may cast that card without paying its mana cost. If you do, sacrifice ~. Then put the revealed cards on the bottom of your library in any order."

You can't sacrifice spells. Maybe it's a fine mechanic, but it has such a potential to be broken. Cascade was strong enough without reverse cascade being a thing.

If you make the version you just proposed, I would make sure every single one is either odd or even, to prevent "climbing" all the way to the top.

Oh that's right, I was thinking of sacrificing the permanent but forgot that it's still a spell. I'll make sure to prevent some kind of ladder effect.

Other name ideas:

Stir

Bestir

Rouse

Trigger

Spark

Impel

Precipitate

Abet

I think I'm actually leaning towards precipitate, thoughts?

How's this? All commons will now have reminder text.

Tremor is far powerful that Cascade and seems inherently broken. A Sorcery who only ability is Tremor is playable by itself. Attached to an actual effect it seems broken. Cascade itself was incredibly powerful and Tremor seems to be an inherently broken mechanic. I'd either change it back to Cascade or make it a Kicker variant.

How's this?

Or I could reuse Ripple.

Now a ripple variant.