Some very creative and clever fans of Katalepsis have designed various MTG cards based on the story! A selection can be found below, both images and cards as text. Spoilers are of course everywhere, so be warned!
Lands by casualCranium:
Cards by crystalcat:
Subtract Existence UB
Target creature phases out. Put a -1/-1 counter on it as it phases out in this way.
I slotted the last number into place. Reality collapsed.
Unearthly Tutor 2BB
When Unearthly Tutor enters the battlefield, draw a card.
If you would draw a card, instead search your library for a card, put it into your hand, shuffle, and lose 3 life.
7: Sacrifice Unearthly Tutor.
Do not call up what ye cannot put down, for a door Outside is more easily opened than closed.
Abyssal Adaptation BGU
Enchantment – Aura, Rare
When Abyssal Adaptation enters the battlefield, draw a card.
Whenever you look at your library or draw a card, choose an ability from among flying, first strike, deathtouch, hexproof, lifelink, menace, reach, trample, and vigilance. Enchanted creature gains that ability until end of turn.
In a world of pure thought, those who think fastest thrive.
Gestating Unknown 2B
Enchantment Creature – Horror Egg, Rare
BB: Sacrifice a creature you control. If a creature sacrificed this way would be put into a graveyard, exile it instead.
3BB: Destroy target creature. If a creature would be destroyed this way, exile it instead. Activate only as a sorcery.
At the beginning of your upkeep, if there are three or more cards exiled by Gestating Unknown, transform it.
…next to that giant sticky black cocoon. A deep bass thrumming echoed inside my own head, a rhythm in the air itself, the heartbeat of a whale.
(⚫) Creature – Horror
Ward – Discard two cards.
Whenever Hatched Neophylon deals combat damage to a player, that player discards a card. If they can’t, they sacrifice a nonland permanent and lose 3 life.
The bundle of tar-black limbs and quivering feelers twitched and writhed on the ground – and something drew a first breath.
Unclosed Insight UUBB
Whenever you draw a card, you lose 1 life.
Whenever an opponent draws a card, draw a card.
A mind is a terrible thing to open.
Seven-Shades’ Gift WW
Target creature you control gains soulbond and “As long as this creature is paired with another creature, that creature gets +1/+1.”
Put a +1/+1 counter on another target creature you control, and that creature gains indestructible until end of turn.
Pair both target creatures.
“A final mask,” she said. “For when all others are removed.”
Blasting Scrutiny BB
Target opponent reveals their hand. You choose a nonland card from it. Exile that card. You and that player each lose 2 life.
To be known is not always a positive experience.