I know there's been a lot of talk about elegance round these parts lately, but I think we ought to keep in mind that the main reason to add and remove cards from your cube is to make the format better.
Keywords are mostly irrelevant to this. Exploit doesn't make your format any better or worse, thought Sidisi might
(I think she makes it better, fwiw). The complexity comes from what the cards actually do, which is barely affected by whatever comes before italicised text.
There is some merit in keywords that aren't spelled out, as you mention with hexproof. No matter how many random one off words are on the cards, if your players can actually take in the information by just reading all the cards, then they'll manage.
There are some exceptions like flying and trample, which I don't think hexproof is on the wotc list of? Those cards just seem to need the space.
I wouldn't worry too much. Give your players the tools to learn and shortcut where they can, and they'll manage.
Now that all said, let me offer my thoughts:
One instance
- level up: Student of Warfare ---> Totally fine. If there's one thing gamers grok, it's leveling
- battle cry: Rooftop Sentry ---> Should be alright, battle cry is simple. Doesn't this guy have batallion as well?
- echo: Thraben War Marshal ---> I'm just not a huge fan of this effect to be honest. Theres other ways to make 2 dudes, and given this is custom already, I think you can do better than middling time spiral commons. May I suggust "Get em Boys" from my cube?
- outlast: Abzan Falconer ---> Honestly I think this card has outlasted ones of times in my cube, but I still think it's better to run this than a more elegant custom. The power level's basically where I want it to be (Which may or not be true for you) and customs kinda inherently have a bit of inelegance to them, since no matter how amazing your design is, it can't be as natural to even middling cards from a recent-ish set, since people are familiar with those.
- awaken: Clutch of Currents > shit, found another instance... ---> Yeah fuck awaken. This is blue haste (Which I don't have a problem with where I think it's needed, but this is mostly just power level concerns), unsatisfying kicker because decks here probably aren't 18 land affairs, and the unkicked version of this spell is REALLY bad. Toss em.
- flip cards: Nezumi Graverobber ---> Eh, I think he's had his time in the sun. It's graveyard hate, but more often then not this is a level up creature where you don't know how many activations you'll need, and the frame is super aggravating. I'd toss it.
- exploit: Sidisi, Undead Vizier ---> This card is rather unique in what it does, the body, and it's also on the short list of good black 5s. Sure, exploit is barely even a mechanic, but don't let that stand in the way of you adding a great magic card to your cube.
- split cards: Life // Death ---> I personally don't like this card because all life does is kill people, so it's essentially like adding a lava spike // reanimate split card, and I don't have a huge love for reanimate either. That being said, there's basically no mechanic more intuitive than split cards. It's just two cards, but in one card I think the only question you'll ever get on these is "Can I play both?" where anyone at the table says no, and after those 5 words are exchanged everything is smooth.
- renown: Goblin Glory Chaser > Monastry Swiftspear ---> Renown is a fine mechanic. People get it, and it does answer the one question people usually have right there (Does it keep getting bigger?). That being said, I don't love this card, and I'd add Stromkirk Noble instead anyday, since he's A) a cool little check on sometimes lesser known creature types ("Oh man mutavault is a human, dang!") and B) actually represents a dream for your players. He's about the only successful "protect a threat" creature I've run that has actually panned out, so I'd do that instead (or double up on it, like I have)
- unleash: Gore-House Chainwalker > Borderland Marauder ---> Again, unleash is really short and sweet, and these are the kind of cuts I disagree with. Unleash is fine, offers a bit of flexibility, and isn't as easily replaced with say, a second copy of War-Name Aspirant (who has the dumbest name ever).
- bloodthirst: Stormblood Berserker > Immobilizer Eldrazi ---> Much like unleash, this is a pretty simple thing here that makes sense, gives your drafter a plan, and performs well. Now, you might actually want immobilizer eldrazi for other reasons, but I'd cut something else
- escalate: Collective Defiance ---> No reason to cut this for complexity. Kicker --> Choose another is basically the lovechild of half of all magic spell mechanics, your drafters will be fine with this
- proliferate: Volt Charge ---> This one is a bit more contentious. The mechanic itself is simple, and it does let your drafters go on a quest (Kinda like seeing goblin king in a pack, you know?) But on the other hand, it's pretty clearly the only playable proliferate spell, and a lot of the creatures that involve +1/+1 counters (the easiest possible synergy) aren't that interesting on their own (Nothing like Thalia, Snapcaster, or even imposing sovereign ever has +1/+1 counters on it since just setting their power/toughness takes up so much of the text box already). I've reacted to this by making more proliferate spells and more +1/+1 counter dudes, but maybe that tax isn't worth it, and cool as it is ole 'chargy here should stay on the bench. That kind of depends on what your format wants, and how deep people expect volt charge to be. If their expectations and your intention are that they can draft a deck where EVERY creature has counters on it and volt charge is absolutly amazing, that's obviously very different than it being added as a 23rd card quality burn spell that occasionally interacts in cool ways with 3-4 creatures in your deck.
- convoke: Stoke the Flames ---> Convoke is a bit odd, and does give drafters some pause. This could go, especially since I'm not sure how purely necessary an instant speed 4 damage burn spell is.
- delirium: Gnarlwood Dryad ---> I've tried delirium in my format and I didn't like it. This might be a candidate for removal just given how much of an environmental change it takes to make this a reasonable goal. I do like the 1/1 deathtouch with lategame value as an attacker idea though, so maybe there's a custom idea there? (For reference, I don't think nimble mongoose is at all a card)
- bestow: Boon Satyr ---> Bestow has it's fair share of rules headaches (Can I negate this guy?) which can mostly be easily avoided (Negate not being in the cube), and since this is technically kicker, it plays well. Not a huge ammount of gain, but green 3s being as anemic as they are, you might feel the hit cutting this guy. I have, but I wouldn't fault you for going either way.
- affinity: Umoru, the Earth Enraged ---> Just change it to costs 1 less for blah blah blah. Realistically you aren't adding any more affinity cards anyways However, if your drafters are usually longtime players that don't know new mechanics rather than the reverse, I'd actually keep it, since affinity has kind of entered the magic lingo despite being on 0 relevant cards now, much like hellbent
- shroud: Lightning Greaves ---> Shroud is fine, but lightning greaves is uninteractive and swingy, so there's better reasons to cut it than keyword nonsense
- exalted: Qasali Pridemage ---> Exalted might not be in a lot of places, but people love it. Another simple thing that adds a decent amount. Keep him!
- persist: Kitchen Finks ---> Finks does a good batterskull impression in terms of powerful cards that leave you open to a large number of decks, but persist is not a reason. Even in a format where +1/+1 counters are a big part, people get persist. There's reasons to cut it, but keywords aren't a concern here.
- retrace: Worm Harvest ---> I've got other concerns with this card, but I'll actually give it a pass since it feeds to well into itself.
- dethrone: Dack's Duplicate ---> Cool card, love it, but there's not much reason to keep it around. Not like UR are the creature colors anyways, so I don't think anyone will really mourn the loss. Also, given how this card plays in comparison to the +1/+1 counters aggro deck, it doesn't really count as support, which can confuse your drafters, who pick this card up to go alongside a pile of Stromkirk Nobles and Abzan Falconers, where it actually never gets a counter
- cascade: Etherium-Horn Sorcerer ---> Eh, cascade is fun enough that drafters will put in the work That being said, unless this card is a fan favorite, I'm not actually a huge fan, given how expensive it is and the weird ways it contorts your blue deckbuilding (No counterspells, x spells, etc)
Two instances
- bolster: Elite Scaleguard and Dromoka, the Eternal ---> Again, people get it. I think scaleguard is either horrible or wins you the game, so it can go for other reasons (I'm cutting it when I get around to patching)
- hideaway: Windbrisk Heights, Shelldock Isle ---> The cons here are how swingy these cards are, and that the part where they ETB tapped is PART OF THE HIDEAWAY RULES TEXT WHY WIZARDS. The pros are that these are really appealing lands that give you a goal and card advantage in a sweet way. I could go either way.
- fading: Parallax Wave, Tangle Wire ---> I don't think I've ever seen a tangle wire game where someone wasn't absolutely miserable, but hey, that could be your jam Wave is fine, and another decent thing to proliferate, and plays well. The only complaint I have with the thing is that Vanishing (See Calciderm) makes WAY more sense.
- delve: Dig Through Time, Tasigur, the Golden Fang ---> Assuming you're okay with the power level of these cards, keep em! Delve is something where you really don't want there to be 30 cards in your cube that have this mechanic.
- madness: Asylum Visitor, From Under the Floorboards ---> Floorboards seems a little loose, given how much of the card is madness bound, but visitor is fine. even if it never comes up, the focus of the card is on the later half anyways, so people usually gloss over the madness anyways.
- converge: Painful Truths, Radiant Flames ---> Eh, up to you. If these become Read the bones and anger of the gods I don't think people would mind, scaling aside
- ferocious: Crater's Claws, Heir of the Wilds ---> It makes sense and it's not hiding any rules text at all, it's just there to connect things like landfall. totally fine.
- monstrosity: Polukranos, World Eater, Fleecemane Lion ---> Monstrosity is one of those odd ones. It's the only creature ability you can actually counter with doom blade, but on the other hand there's really nothing like polukranos. They'll probably come back to this mechanic eventually, and other than the doom blade issue it plays well (Post Hoc Kicker). Not a huge fan of lion in concept though.
- landfall: Undergrowth Champion, Invigorating Overgrowth ---> Eh, up to you. Landfall is another magic lexography thing now, so people will understand.
- fight: Epic Confrontation, Dromoka's Command ---> How friggin dare you Fight? FIGHT? This is as intuitive as it gets, is hardly a keyword, and we were screaming for it to actually be a keyword for so long!
- scavenge: Dreg Mangler, Varolz, the Scar-Striped ---> Eh, I've never really found this mechanic to be that great, but people understand it: Creature flashback as an aura. I'm closer on dreg mangler, but I wouldn't be sad.
- meld: Hanweir Garrison, Hanweir Battlements ---> hotly debated certainly keep it in for the dream if battlements is actually good enough, but if you're only running one of them, then I might make a custom. Garrison is such an odd creature: it's a building, but it can attack, and it makes dudes, all on top of the weird meld text which might actually be distracting.
Three instances
investigate: Bygone Bishop, Declaration in Stone, Tireless Tracker ---> Investigate plays too well in small numbers to be trimmed. Again, like delve this isn't a mechanic you want 30 cards with, since you'll end the game with clues uncracked.
evoke: Reveillark, Mulldrifter, Shriekmaw ---> Maybe lark, but these all play too well and are too intuitive to let go on.
raid: Bloodsoaked Champion x2, War-Name Aspirant ---> "Have you attacked". Yeah you're fine.
dredge: Darkblast, Life from the Loam, Shambling Shell ---> If loam was the only card I'd still say it was fine since it feeds into itself so well so you understand it. Personally I think the other two are just a bit weak
dash: Lightning Berserker, Zurgo Bellstriker, Goblin Heelcutter ---> Again, this plays into a pretty core red idea of temp benefit. Keep em.
living weapon: Spark of Redemption, Mindcarver, Bonehoard ---> god I wish this was easier. Living weapon is so bloody complicated, and you get so little room to have any rules text on the card once you've got the reminder text there that I kind of hate it. But creature --> equipment is a line that really feels right, and players love em. It depends on what you're letting in here. The only living weapon in my environment is +2/+2 and flying, so I don't think it's worth it. But if you have something that's really jumping out at you design wise, keep em.
Other
evolve: Cloudfin Raptor x2, Experiment One x2 > keep all four or keep none. ---> I vote keep. I like giving drafters direction, and evolve certainly does that. It's a solid growth mechanic, which is also nice, and rewards good sequencing. The only weird things are creatures that ETB with counters (The old
Reverent Hunter vs
Cytoplast root-kin oddity from when I was bitching about experiment two) and clones (which actually makes sense, since clones would die if they ever were actually a 0/0, so clearly they evolve with their new P/T)
hexproof: Sphinx of the Final Word, Fleecemane Lion, Narset, Enlightened Master > none of it spelled out ---> Eh fuck hexproof anyways. None of these cards even seem worth the gameplay downsides, let alone the complexity ones
double strike: four hits, among them the only level up creature Student of Warfare ---> People understand this. there might be some issues where they're like "when does the damage happen?" but like split cards, with that one issue out of the way these cards are totally fine.
?
generating land with Land A cycling, and Land B cycling, maybe for 1 hybrid mana A/B
