it's been a long time since we did a flavor round and this is very much a flavor card, so let's go with make a card that represents a pivotal moment in a larger narrative. probably helps to namecheck specific places and/or people but you don't have to.

gonna start grades on Friday. go!

That card is spectacular. Just sublime.

Modify the Scroll
Sorcery (R)
Target player reveals their hand. You may choose a nonland card from that player's hand or graveyard. If you do, that player casts that spell if able and pays life equal to its mana value rather than paying its mana cost. If a spell wasn't cast this way, draw a card and return this spell to its owner's hand.
"They are all my pieces, Jace Beleren. They always were. I just no longer want to play."
-Emeria

Edit: Tweaked the card a bit to feel slightly less useless.

yeah I miss JV

I was thinking about going full Universes Beyond but it seems fairer if the card is trying to tell an original story rather than evoking one that already exists

Birth of the New Regime

Sorcery
As an additional cost to cast Birth of the New Regime, sacrifice X creatures.
Each opponent sacrifices X creatures. Put X +1/+1 counters on up to one target creature you control.
Joseph Kastov betrayed his king, betrayed his ideals, betrayed his followers, and claimed everything for himself.

Are EDH-only cards okay?

Negligence
Enchantment
When ~ enters, exile target nonland permanent until ~ leaves the battlefield.
When ~ leaves, sacrifice a nonland permanent you control.
By sealing Nahiri away in the Helvault, Sorin had consigned both of their homes to ruin.

I broadly prefer cards that are intended for standard-legal sets but I've accepted some Commander references in the past so I'll say I don't mind but I'll be considering balance in the same way regardless of the intended format.

Then I will stick to something standard then. Was thinking of 'if an opponent lost this turn' ability but that's really only applicable to multiplayer formats.

Day of Revelation -
Sorcery
Until end of turn, whenever a creature you control attacks, create a 1/1 white Soldier creature token tapped and attacking. If this spell was foretold, create a 4/4 red Dragon creature token tapped and attacking instead.
Foretell

Oath of Pursuit
Enchantment (R)
Creatures you control have Haste.
At the end of your turn, if no creatures you control attacked this turn, you lose the game.
Their Oath shall drive them, and yet betray them, and ever snatch away the very treasures that they have sworn to pursue.
- The Silmarillion, J. R. R. Tolkien

Edgar Markov's Blasphemy
Sorcery (R)
Destroy target creature. Create a 2/2 black Vampire creature token. If the destroyed creature was an Angel, put two +1/+1 counters on the token. If the destroyed creature was white, put a lifelink counter and a menace counter on the token.

For As Long As We Both Shall Live
Enchantment - Aura (U)
Enchant two creatures
If one of these enchanted creatures leaves the battlefield, the other leaves in the same manner. (Examples: If one is put into its owner's library, the other is put into its owner's library; if one is put into its owner's hand, the other is put into its owner's hand; etc.)
"With the powers vested in me by the authorities of Ulgrotha, I now pronounce you—"
—Hazduhr the Abbot, final words

Galactic Harvest |
Sorcery

Mill your library, then shuffle each noncreature card in your graveyard into your library.
Exile ~.

"You exist because we allow it, and you will end because we demand it."

Syndali Offers Her Blood —
Sorcery (R)
As an additional cost to cast Syndali Offers Her Blood, pay X life.
Draw X cards.
“What happens now?” Mocoth stared dispassionately into the bubbling cauldron.
“We wait.” Syndali's lips betrayed half a grin as she watched the elixir begin to brew.

Double Agent
Enchantment - Aura (R)
You may cast this spell without paying its mana cost if it targets a creature you own.
Enchant creature
You control enchanted creature.
"You made me blow my cover!"

On a side note, is there a mechanical difference between "Cast this spell without paying its mana cost" and "You may pay 0 rather than pay this spells mana cast."? Scryfall has a mix of both across all manner of spells.

im pretty sure this event already has a card associated with it but whatever

Arrival at Kingsbridge
Sorcery (M)
Put a creature card from your hand onto the battlefield. If that creature is legendary, other creatures you control get +X/+X until end of turn, where X is that creature's power.
Krugnar Oathbreaker strode forth. He bellowed a challenge to the cowards hiding behind their gleaming white walls, and his assembled warclan echoed a chorus behind him.

I think the latter is mostly used for things like archive trap that are meant to fit into broader formatting conventions.

gonna start grading now, no more edits please.