I haven't seen the finale yet, so this isn't about that. I'm still back at episode 100, but I'll try to get through the rest of the season and post my thoughts about it when I have. In the meantime, FanofMostEverything's Twilight, Time-Snared card from the other thread gave me some 4 AM ideas for Time Loop Trilogy cards. I haven't played Magic in a dog's age, so I have no idea of how over/underpowered these would actually be, but here goes:

Unremarkable Flower Vendor
Summon Creature- Pony
G1
1/1

During your upkeep, you may pay B and exile Unremarkable Flower Vendor from your graveyard. If you do, put a 3/3 black Changeling token into play under your control.

Don't worry. You won't be missed.

Post-Timeloop Stress Disorder
Enchant Creature
U

When enchanted creature's controller plays a spell, put a -1/-1 counter on this creature if there already exists a copy of that spell in their graveyard.

Please, no. Not again.

Star Swirl
Summon Creature- Pony
UU
4/4

At the end of your turn, if Star Swirl attacked this turn your opponent may gain control of target creature other than Star Swirl that also attacked this turn.
At the end of your opponent's turn, if Star Swirl blocked this turn your opponent may gain control of target creature other than Star Swirl that also blocked this turn.

To his enemies, he is suffering incarnate. To his allies, he's just insufferable.

Shooting Star
Summon Creature- Pony
UR
2/2

Whenever you play a spell, draw a card. Then discard a random card from your hand.

No more studying! I wanna go on an adventure!

Paradoxical Creation
Sorcery
U

Search your library for an artifact with casting cost of X or less and put it into play under your control. X is equal to the number of experience tokens you've acquired from Twilight, Time-Snared.

Note to self: Go back in time and design Paradoxical Creation card.

Regalia of Harmony
Artifact
[7]

Whenever an opponent plays a creature you may flip a coin. If it lands heads, destroy that creature.

Sacrifice a creature: Redo target coin flip.

Better luck next time. We promise.

Cloud Kicker
Summon Creature- Pony
[R][W][2]
2/3

If Cloud Kicker deals combat damage to or is dealt combat damage by a creature with the [Pony] type, prevent that damage. At the end of any turn in which damage was prevented in this fashion, put a +1/+1 counter on Cloud Kicker.

On a good day, she takes a licking and keeps on ticking. On a great day, she takes a fondling, a caressing, and a number of improbably large objects as well.

Forced Transformation
Sorcery
WWB3

Take control of all creatures with the [Changeling] creature type. Put a -1/-1 counter on each of them, and their creature type becomes [Pony]. If any creature is reduced to below 1 power by Forced Transformation, destroy it.

They aren't called the Elements of Niceness

Queen Sparkle
Legendary Creature- Changeling
UBB3
7/4

While Queen Sparkle is in play, skip your draw and discard phase.

When Queen Sparkle enters play, exile Twilight, Time-Snared from the game and draw your entire deck.

So many options, so little time.

Queen Chrysalis
Legendary Creature- Changeling
BBRR2
5/5

If a creature dies on a turn Queen Chrysalis dealt combat damage to it, put a black 3/3 Changeling token into play under your control.

Sacrifice a creature: Put a black 3/3 Changeling token into play under your control.

If you thought you could defeat me, your brain must not be working properly. Luckily I still have a use for it.

4884317
I apologize in advance, but I am compelled to properly format and critique these.

Unremarkable Flower Vendor 1G
Creature — Pony
At the beginning of your upkeep, you may pay B and exile Unremarkable Flower Vendor from your graveyard. If you do, put a 3/3 black Shapeshifter creature token named Changeling onto the battlefield.
Don't worry. You won't be missed.
1/1

No major issues with this one. It's interesting to compare it to Centaur's Herald. Given the small size and black synergy, it's just begging to be sacrificed. How appropriate. As for changelings, sadly, Magic already has some, and they're Shapeshifters. (Technically, they're everything, but that's what's on their type line.)

Repetitive Stress B
Enchantment — Aura
Enchant creature
Whenever enchanted creature's controller casts a spell, put a -1/-1 counter on enchanted creature if that spell has the same name as a card in that player's graveyard.
"Please, no. Not again."

This one has two key issues, one major one minor. Irrespectively, its name is too long and it isn't blue. At least, not anymore. It's been a long time since the days of Unstable Mutation. The effect itself is a bit niche, but would actually work quite well against more competitive decks.

Star Swirl 2U
Legendary Creature — Unicorn Wizard
Whenever Star Swirl attacks, defending player chooses another target attacking creature. That player gains control of that creature at the beginning of the next end step.
Whenever Star Swirl blocks, attacking player chooses another target blocking creature. That player gains control of that creature at the beginning of the next end step.
To his enemies, he is suffering incarnate. To his allies, he's just insufferable.
4/4

If anypony is legendary, it's Star Swirl. (Though I suppose multiples do show up in the same place at times...) The creature typing is something of a matter of personal preference, but he's pretty clearly a unicorn and a wizard. The key issue is that you can have more than one opponent at a time, so I had to rejigger the triggers to let the game remember who else was involved combat in terms of both players and creatures.
There was also something of a power level concern. A 4/4 for two that effectively has to attack alone is not that big a deal, especially not if the deck has exalted effect, hence the cost increase.

(Shooting Star) UR
Creature — Unicorn
Whenever you cast a spell, draw a card, then discard a card at random.
"No more studying! I wanna go on an adventure!"
2/2

Blue and red are the worst creature colors, so giving them a potent utility bear—that is, a 2/2 for two that also does stuff—is a bit much. The random discard does lessen matters somewhat, but this is still probably pushing the envelope. On a less critical matter, nonlegendary creatures shouldn't have specific names; they're meant to be somewhat generic. Granted, making Shooting Star legendary would assuage the power issue a bit...

Paradoxical Creation U
Sorcery
Search your library for an artifact card with converted mana cost X or less, reveal it, and put it into your hand, where X is the number of experience you have. Then shuffle your library.
Note to self: Go back in time and design Paradoxical Creation card.

I can sum up the original design in one word: No. No for several reasons. The card's design is parasitic in extreme; it's almost completely useless without Twilight. (Granted, it can fetch Moxen, but still.) With Twilight, it is terrifyingly abusable. When your card is inviting comparisons to Tinker, you have a problem. The adjustments still leave a narrow but powerful card, but one with a bit more usability.

Also, this segues nicely into another one of my creations:

Home Run, Dear Companion 3
Legendary Artifact — Equipment
Equipped creature gets +1/+1 for each experience counter you have.
Equip 3

Regalia of Harmony 7
Legendary Artifact
Whenever an opponent casts a creature spell, flip a coin. If the coin comes up heads, counter that spell.
Sacrifice a creature: The next time you would flip a coin this turn, instead flip two coins and ignore one.
Better luck next time. We promise.

Technically speaking, Goblin Bookie doesn't work, since you can't use spells or abilities in the middle of an effect's resolution. As such, I tweaked this to a Krark's Thumb-like effect. I also made it legendary, since a. Elements of Harmony, and b. exceptionally unfun in multiples. Given the confusion between spells and permanents, it's possible that this isn't doing quite what you intended it to. If that's the case, the first ability should be "Whenever a creature enters the battlefield under an opponent's control, flip a coin. If the coin comes up heads, destroy that creature."

(Cloud Kicker) 3W
Creature — Pegasus
Flying
Prevent all combat damage that Cloud Kicker would deal to or be dealt by Pony, Pegasus, and Unicorn creatures. Whenever damage is prevented this way, put a +1/+1 counter on Cloud Kicker.
On a good day, she takes a licking and keeps on ticking. On a great day, she takes a fondling, a caressing, and a number of improbably large objects as well.
2/2

Giving pegasi flying is kind of important, if only to avoid Whippoorwhill Syndrome. Also, ironically enough, there's nothing really red about this Cloud Kicker. Damage prevention and +1/+1 counters both fall under white's bailiwick. The lack of afterglow in the ability is more to prevent memory issues than to imply anything about Cloudy's performance. And, again, specific names on nonlegendaries are a no-no.

Forced Transformation 3UB
Sorcery
Gain control of all Shapeshifter creatures. They become Ponies. Put a -1/-1 counter on each of them, then destroy all creatures you gained control of this way with power 0 or less.
They aren't called the Elements of Niceness.

Gaining control of creatures is one of blue's greatest weapons. The narrowness of the effect, weakening of the creatures, and multicolor cost mean that this need only cost five.

Queen Sparkle 8UUUU
Legendary Creature — Shapeshifter
When Queen Sparkle enters the battlefield, draw cards equal to the number of cards in your library.
Skip your draw step.
You have no maximum hand size.
"So many options, so little time."
7/4

It's been a long time since the discard phase was a thing. Name-specific effects generally shouldn't be done in Magic, even when flavorfully appropriate, and without that exile effect, Queen Sparkle actually isn't black. As for that enter the battlefield trigger, Enter the Infinite costs twelve and only gives you one untap step to do something with the results. I'd say this is being generous in the extreme.

Queen Chrysalis 3BBB
Legendary Creature — Shapeshifter
Whenever a creature dealt damage by Queen Chrysalis this turn dies, put a 3/3 black Shapeshifter creature token named Changeling onto the battlefield.
Sacrifice a nontoken creature: Put a 3/3 black Shapeshifter creature token named Changeling onto the battlefield.
"If you thought you could defeat me, your brain must not be working properly. Luckily I still have a use for it."
5/5

Chrysalis, meanwhile, is all black. Only one other adjustment was needed. Without that "nontoken" rider, you could sacrifice changelings continually, which would be an instant win with cards like Blood Artist.

4884550

The difference with Twilight is she's a 4 toughness with 0 protection, so if you zap her then they instantly lose at the start of their next draw phase, so I'd argue she's a bit different than the sorcery there.

And jeez, Magic's rules have changed a ton it seems - it's looking like they've dialed back a lot on how often you can interrupt things.

4884550

Blue and red are the worst creature colors, so giving them a potent utility bear—that is, a 2/2 for two that also does stuff—is a bit much.

But on the plus side, "Potent Utility Bear" would be a great name for a band

4884800
You're still drawing your whole deck, which includes any copies of, say, Turn Aside you may have. Or cards like Leashling or Reminisce that could restock your library. Or even Laboratory Maniac, to turn Queen Sparkle's death into victory!

Interrupts are no longer a thing. It's all instants now. Eakin just didn't make any. And technically speaking, Goblin Bookie never worked.

4885210
I'd listen to them.

4885270

The thing I remember is they did something screwy to the stack, so like for example Morphling is now no longer stupidly good, and so on.

4886909
Yeah, combat damage no longer uses the stack. No giving Morphling umpty-lump jillion toughness while its sky-high power is waiting to hit something.