cute card, let's go with make a piece of removal whose mechanics and flavor tell a story. as you can see from the prompt card the removal doesn't have to be permanent, although it certainly can be.

grading starts Friday. go!

Knife in the Back
Instant
Target creature gets -3/-3 until end of turn.
Search your library for an equipment card, reveal it, put it into your hand, then shuffle.

Crooked Prosecution

Instant
As an additional cost to cast Crooked Prosecution, you may Collect evidence 3 X times. (To do this, Exile cards with total mana value 3 or greater from your graveyard X times.)
Detain target creature or Planeswalker. If evidence was collected, instead exile it unless its controller discards a card and/or sacrifices a clue a total of X times.
From the right position, truth can be fabricated more easily than it can be found.

Parasitic Incubation
Enchantment - Aura
~ costs less to cast as long as you control an insect.
Enchant creature.
Enchanted creature can't attack or block and it's activated abilities can't be activated.
At the beginning of your upkeep, destroy enchanted creature. If you do, create a 1/1 black and green Insect creature token.

Mari's Mark
Enchantment - Aura
Enchant Creature
When Mari's Mark enters, surveil 3. (Look at the top 3 cards of your library, and put any number of them in your graveyard in any order, and the remainder on top of your library in any order)
Whenever an assassin, mercenary, or rogue enters under you control, destroy enchanted creature

Gone Tomorrow
Sorcery (R)
You may skip your next turn rather than pay this spell's mana cost.
For each creature without vanishing, put a number of time counters on it equal to its mana value. Those creatures gain vanishing.
Here today...

Eaten by Worms
Instant
Destroy target creature. At the beginning of the next end step, if that card is in a graveyard, exile it, and create X 0/1 black Worm creature tokens, where X is that card's toughness.
"You'll be back? Parts of you, maybe."

Head-On Collison
Sorcery

Target creature you control fights target creature you don't control. If your creature is a vehicle, prevent all damage that would be dealt to it in this fight.

The offender pleaded guilty to manslaughter. Not because of intent, but because it sounded cooler.

Mark for Death —
Instant (U)
Destroy target creature. If you control an Assassin, create a Treasure token.
“Everybody dies. We in the Cold Circle just bring some people to Death's door a little sooner, that's all.”
—Morgethai of the Hungry Dagger

Overran Courtyard -
Enchantment - Room
Create three 1/1 Citizen creature tokens with haste. Creatures you control gains trample until end of turn.
Trampled plants and footprints in the mud laid testament to the violence that transpired here.
==========================
Bloodstained Office -
Enchantment - Room
Target opponent sacrifices the creature they control with the highest mana value and creates a treasure token.
The smoking gun on the desk and blood splatter on the window tells of how the tale ended.

Looming Sword
Enchantment - Aura (U)
Enchant creature
When enchanted creature attacks or blocks, sacrifice this enchantment, and this enchantment deals 4 damage to it.
Indecision is a kind of a death on it's own.

Usurped
Enchantment - Aura (U)
Enchant creature
Whenever a creature with power greater than enchanted creature enters, attach Usurped to it and sacrifice this creature.
His brothers words whispered in the night. "You will gain the crown as I did, and lose it the same way."

Princess Isabella, Temptress of Men

Legendary Creature - Siren Noble
When Princess Isabella, Temptress of Men enters, two target creatures an opponent controls fight each other. Then gain control of one of them for as long as you control Princess Isabella. (To fight, each deals damage equal to its power to the other.)
She enjoys pitting the men of court against each other in competitions for her favour: courtier against courtier, friend against friend, brother against brother. The deeper the bond, the sweeter the treachery.
2/2

Study Abroad
Enchantment (U)
When Study Abroad enters, exile target creature an opponent controls until Study Abroad leaves the battlefield.
, Sacrifice Study Abroad: Draw three cards.
Any young citizen of Steelhold showing a talent for the arcane is sent to the academy in Rukt to hone their skills. It's a great opportunity for those selected—and if they so happen to choose not to come back, it's that much less trouble for the Enforcers.

starting grades!

feels a bit disjointed. I wish it did something with an equipment already in play rather than tutoring, 'cause when you use a knife to stab someone, you don't usually wind up with more knives. there's also a bit of the snake-in-boots problem where just over 1% of equipments are knives, so this is much more likely to get a hammer or something, but that's par for the course on these. the mechanics also don't feel that connected: they both work and provide value, but it's not clear why they're on the same card.
2/5

if I do the collect evidence thing and they do pay the cost, is the creature still detained? as worded I'm not sure, although I think not. probably better if it is. honestly I think the detain might be better off left off the card: lyev decree says this isn't very powerful if you don't collect evidence, and then once you do it's such a fiddly minigame that having the extra (and usually irrelevant) detain rider feels distracting. beyond that, the game of the card seems solid, but the story of it is resting pretty heavily on keyword names that are, themselves, kinda forced. (mostly collect evidence, the other two make more sense.) there's also a mechanical issue: none of the collect evidence cards they've printed let you do it a variable number of times, and I think that's for a good reason: if my graveyard is two 6-drops, how many times can I collect evidence 3? anyway I think there's a good version of this but it got a little lost in the weeds.
2/5

golgari arrest is odd, but in practice it only lasts one turn so it's probably fine. I like the idea but I think it's maybe going in a bit too much on the story, which results in a lot of text. maybe if you dropped the cost reduction thing and instead made multiple tokens?
3/5

cute! the surveil is a solid utility, and otherworldly gaze says it's strong enough on a 1-drop that you don't feel cheated if you don't immediately have the follow-up for the kill. it also makes it proactive enough that you're likely to want to run it out early, even though this can be pretty serious removal later on. dunno about the overall power, a 1-mana murder is very strong but this is sorcery speed and takes non-trivial work, both in deckbuilding and in play, so I think it's fine, at least as a first guess since we can't playtest.
4/5

I like the first ability a lot. I wish the rest of it delivered on it. as a sweeper, rushing it out early isn't all that useful since they're unlikely to have as many targets, and as a sweeper that mostly doesn't kill things right away anyway it can't even do the doomskar thing where being playable early can save you if they do have a super blitzy start. it also does nothing against tokens, since vanishing has no effect if you never get a time counter in the first place. I think there's potential here but I'd swap out the main effect for something a little more meaningful.
3/5

I'm not 100% sure this works, since the way the rules currently handle split permanents is to simply remove all text from the locked side, but there's probably a way to corner-case this in if they wanted to. (I also don't know if you can put counters on phased-out permanents? but again the rules can just say you can and it's fine.) I don't know how I feel about a room card where only one side is viable to play first, feels like it kinda loses the fun of a split card. this isn't quite that, since you can use Dungeon to steal a thing that's phased out for a different reason, but given how strong a punishment the lock condition is if phasing is common in the environment I assume that's not the intention, and also as worded Floor only worked on etb, not unlocking, which would obviously be fixed and I'm not worried about but figured I'd mention. I dunno, I want to like it but I think the play pattern it requires seems to miss what I find most interesting about rooms as a concept. I do really like the flavor of it, though, and it's a flavor round.
3/5

I'm trying to parse the mechanical purpose of the delay. it makes a lot of sense flavorfully, but I wish it waited longer so there felt like a real window for them to get the card out of their yard as a counterplay option. I do really like the story here, though, and the flavor text is very well written. it's straightforward in its utility but in a way that still feels really evocative, and while the tokens aren't all that useful on their own, I could imagine a set where worm tokens are enough of a theme to bump this up to premium removal in limited.
4/5

I'm always fascinated to see what you come up with in these contests, 'cause you always swing big. sometimes it works, sometimes it doesn't, but this time it definitely worked. I love both the card and the concept of rock tokens. I might weaken the tokens a bit, maybe remove the cost from the activated ability, drop the damage to 1, and add a sorcery restriction, because a bunch of extra shocks running around can get kinda overwhelming and also the sorcery-speed thing prevents it from jumbling combat math quite as badly, but those are all fiddly things that don't really affect the core of the design, which is very strong.
5/5

lol. love this. flavor's great, card works wonderfully, and has a lot of actual utility without losing its story. no notes.
5/5

more people should be named Morgethai of the Hungry Dagger. that aside it's a good card. strictly better than murder which I didn't think they'd done but looking it up they have a couple times so that's cool. solid rider, minor effect but evocative and impactful. overall very solid.
4/5

dripping with flavor, extremely well done on that. (in practice the Room card format definitely doesn't have room for flavor text, but the names alone do so much work I don't even care.) I do think room designs are at their best when they're more than the sum of their parts, though, and this is a bit disjointed. I guess it clears out a blocker, but if you're doing a token swarm that's not as relevant. the trample's also a little odd on a group of 1/1s: I know it applies to the rest of your things as well, but it still lines up strangely. maybe you could tie them together if Office looked for the highest toughness instead, to at least thematically resonate with the trample? dunno. overall I love the story, the mechanics are fine but I'm not quite sold.
4/5

I feel like there has to be a better way to word this but I get what you're going for and I like it. solid, straightforward, but effective. interesting how it plays as a toughness-based pacifism, and the Damocles narrative is pretty clear.
4/5

good catch on the may, I was all set to mark you down for the existence of cho-manno, revolutionary but you beat me to it. I'd still probably just say "Deal 1 damage to target creature X times, where X is that creature's toughness" to avoid some sort of weird combo case I can't think of right now, but that's neither here nor there. flavor's very well written, and the card ties into it well. I wonder how practical it is in its current form given how many decisions it technically force you to make, which causes problems for MTGO and Arena, but the intent is pretty clear.
4/5

huh. I'm not really sure what to make of this. flavor's excellent, and the card is very interesting, albeit a bit brutal for 1. put it on an aggro deck's 1-drop and odds are their entire curve self-annihilates. I think it probably wants to cost like 3 or 4 but it's really hard to say without playtesting. on the other hand if it does cost that much does it ruin the minigame of the card? I don't know. it's a tricky one to evaluate but I can't shake the feeling that there's some pretty fundamental issues here in terms of printability.
3/5

I'd probably do this in a different order ("gain control of target creature, then it fights another target creature its owner controls") but seems reasonable. pretty scary in the right circumstance, although an unprotected 2/2 won't be too hard to kill and at least get the stolen creature back. flavor's solid. whole thing feels a bit... I dunno, overwrought? in a way I can't quite put my finger on, but there's nothing about it I actually think is bad. dunno. gut reactions are weird.
3/5

cute! I wonder how many circumstances that activation is actually going to come up in, since you presumably exiled the creature for a reason, but the upside is high enough to sometimes justify it later on, and it's also a good escape if they happen to have removal if you've got enough mana up. (big if on that, considering it costs 6, but still) the story is a little off in that it's their creature doing the studying but you get the cards, but I think that's a reasonable concession to functionality. the flavor's fun too.
5/5

fun round, lotta good cards, giving the win to Tekk! congrats, nominating now, go join the next one.

I was first going to edit in a "pretend there's a rules change that makes this not be infinite", but I managed to find a satisfying wording. Just dealing damage based on toughness wasn't punch enough rules text, plus it works more naturally with healing salve or furnace of rath effects.