In that these made it in after we stopped recording, I'll answer them here:
Do you prefer to go for clean designs or complicated new mechanics?
Do you prefer to complete unfinished cycles or design new cards?
Clean designs, 100%. I spend much of my time
uncomplicating cards, honestly.
The goal for every card I make is strip away as much as I can while making sure:
-It still is powerful enough to be in dialog with the rest of the cards in my cube
-It still ties into the themes I'm trying to support
-It still works as an aesthetic whole
Sometimes I make cycles and sometimes I make one off cards?
Each colors needs in a cube are different, and there's some things I'm confident that every color needs access to (Fixing, draw smoothing, interaction, threats etc) but that isn't true of everything.
Technically my cube does have a "cycle" of smoothing cantrips in Crack the Case/Consider/Tomb Pillage/Ancient Mantra/Tracking, but I don't really think of it that way because there's differing numbers of each, and there's a wider variety of blue and black cards slotted into that mechanical space
what are the design goals for your cube and how do your custom cards help you achieve them in ways regular cards don't
This is a great way to phrase this question, and I tried my best on the pod to talk about custom cards from a more general perspective and less about my cube in specific, so I'm gonna go kind deep here.
Goal one: Synergy
I highly value the decks you draft having some kind of mechanical cohesion beyond just being "An aggro deck" or "a control deck" or "a midrange deck", I'd much prefer your cards interact with each other based on what's in the text box or type line and not just "how good are these, where do they fit in my curve"
Given that desire for synergy based gameplay, two common questions come up:
-What is this card asking of me?
-What is the payoff if I can do what its asking of me?
To make a bold statement with the player brain, ideally none of the cards I'm playing would give a shit about any of the other cards in my deck. You would much rather have cards that are powerful all the time than ones which were sometimes powerful and sometimes not based on like, the number of artifacts you control (Which gasp, your opponent can mess with? Worrying stuff)
The player probably wants
Lightning bolt over
Galvanic Blast every time. But that's really boring.
Custom cards let you modulate the rewards and the asks of a given magic card to where yeah you can pick
lightning bolt, but based on these other 15 cards I have already,
Galvanic Blast might actually be better. (I'm exaggerating here, pick
lightning bolt, but you can see where I'm going with this)
We've all found some sweet card we really loved, but just cost too much or didn't do enough or had some other problem where it couldn't hang with other cards you loved. Custom cards let you run both, and they let you either bring the weaker card up to the power level of the stronger one, or adjust the power level of the stronger card down to where it's not shouting over all the other cards in your cube.
It is extremely rare that there is something so fundamentally good/bad with a card that it can't be modulated up or down to play with other cards you want to play with
It also lets you solve problems of density, where like maybe there are some cool cards to support a deck idea, but they're all 4 drops and you can't run them all in the same deck without your curve tripping over itself, or there's only like 3 cards and even if you get all 3 there's still not a whole deck there.
Goal two: Elegance
To pick a low hanging fruit, raise your hand if you think there's too many words on magic cards these days?
I love magic, and I'm really dialed in to what's going on with this game, but even I think some cards are too much.
Unfortunately, some of those cards are also cool as hell!
Questing beast is kind of an abomination (It's got fake trample because they couldn't give it real trample because of all the other words they jammed on it), but I really like what it does being a hasty green curve topper, a way to pressure planeswalkers and life totals, and also playing well defensively. But you can fix how hard it is to understand with some visual tweaks:
I really like
Adeline, Resplendent Cathar, except for some reason it makes human soldiers, and they wanted it to be better in multiplayer so it uses extra words in the token creation trigger. Also this card having vigilance is mostly irrelevant, and I think it would benefit from a bit more thought being put into should I swing with my 7/4.
Esika's Chariot is one of the sweetest green cards of the last decade because it plays so well on its own AND it gives you this little quest to go on where copying a 2/2 is fine, but what's the sweetest thing you could copy? Hell they were nice enough to let this copy noncreature tokens, so you
can copy like a clue or whatever because you really need to draw a card.
But it's 100% the only thing in my cube that makes 2/2 cat tokens. That is also fixable!
Goal Three: Agency
As a player and game designer, I hate non-games. I do love the amount of variance magic has (having played games with more and less variance) and I know the land system is a good thing.
I don't want anyone to lose in deckbuilding.
I don't want anyone to lose because their top 10 has 2 lands in it, or 8 lands in it.
But I recognize its impossible to eliminate that, so I try and mitigate it wherever I can.
Everyone has the same one card a turn draw step, but
preordain and cards like it help you cheat the dice a little and exert some influence about what you're going to draw.
Problem is, this style of effect is REALLY powerful, especially when it's one mana, so WotC hasn't really printed anything like
preordain in any other color to keep constructed at least slightly different draw to draw.
I don't have that problem, none of my cards are ever going to be influencing the legacy metagame, so I can print whatever I need.
What's more, going back to Goal 1, I can tie them into my synergy decks:
White plays with artifacts and card types, so the clue is important. Black plays with the graveyard, so the mill is important, and often focuses around using a single strong threat multiple times, so it gets the regrowth. Green also plays with the graveyard, but also a lot of green's staple effects are on permanents, so it gets to chose between removal or threats or even filling out types.
Red...often has too many lands

IDK You could certainly tie this into your decks more than I have.
Goal Four: Aesthetics
I mean I think if you don't think this is a goal for your cube, you might be hiding from yourself? Like yeah I'll say it I love this project, and I want it to look good!
I don't have a unified aesthetic theme the way that like, some desert cubes or Roja's rusty box of goblins might, but I still want all the cards to look good from my perspective, and sometimes I like a cards rules text but I don't like the cards art or frame.
So I fix it:
Sometimes a card is great, it does exactly what you want, but it has Dennis Nedry in a plastic branded raincoat in the art.
Sometimes you just think Taigo Chan's original art for snapcaster mage would look dope as hell in the FANG frame from Innistrad: Crimson Vow.
AND YOUD BE RIGHT
Okay that's probably enough manifesto for now