Thanks, both of you! It’s interesting to see how the different perspectives you two had over these games infom your balance suggestions.
Alright, let’s see how things look if we organise your suggestions by spec (I’ll add some thoughts of my own as well):
Black Starter
Neither of you directly suggested any changes to the Black starter deck, but…
The idea of making Mirror Illusions cost $1 to summon and $1 to transform is a good one, but it doesn’t help Aven and it’s a bit inelegant. Instead, if Deteriorate cost $1 to play it would require more from Black than a single card that they can easily get back with Dark Pact (which also costs $0 in the retail game… ) or Garth’s midband, it would be a bit safer for Blue to play heroes early game, and it would make the gold deficit if an illusion is popped not quite as bad (for that matter, sometimes an illusion could actually survive a turn where Black has Deteriorate if money is tight).
Demonology

- Vandy not being allowed to fetch her Ulti
- Dark Pact costing 1g would still be a very good card
- Vandy doesn’t need Resist 1 on midband, it wouldn’t help this matchup though

If nerfing Black, I think Vandy is the biggest offender. It’s the combination of her ability to efficiently ramp up her stats and Deteriorate/Sacrifice’s ability to clear patrollers that makes playing a blue hero on turn 2 so dangerous. That, in turn, increases Blue’s reliance on card plays which, in the face of Blacks’ multiple discard options, makes it easy for turn 1 Black to completely suppress Blue. I’m not sure what the best way to nerf her would be, but the first thing I’d try would be to make her level at 1-3/4-5/6 to slow down that initial rush.
I’ll start by reiterating that if either Deteriorate or Dark Pact were to have their price changed, they need to match each other so Reputable Newsman doesn’t have an even harder time covering what he needs to. I’m of the opinion that both should cost $1, simply because that elegantly fixes quite a few problems.
I think the various Vandy changes are good, and I’m definitely in favor of removing Resist 1 from her midband (I still don’t know why it’s even there, and EricF had suggested it when he was still around). I like only fetching non-ultimate spells with her midband, since that means there’s a bit more setup required to get Metamorphosis working. Making it cost $1 more to get to midband seems good too to reduce the early pressure. I have this vague feeling that all three changes at once is too much, but I’m not sure why… None of them is that big, and they alter the balance of different things. I’d be interested in seeing a version of Vandy tested with all of them to see how it feels.
…Also, neither of you think anything aside from Vandy and/or her spells needs adjusted in Demonology. Makes sense, she’d definitely the most terrifying part of the spec!
Disease
(Obviously a joke, but we all seem to agree that Disease is not part of the balance problem.)
Necromancy

- Garth mid/maxing at 5/8 might help
- Bone Collector could maybe cost 3 and still be pretty good? Less sure about that
The Garth change is probably good. I don’t know if Bone Collector would still be worth using over Hooded Executioner or either of the Disease Tech I units if it were priced at $3, but I’m unqualified to talk about that… I will say that it might be worth testing, if only to let those others see more use.
One thing I’d considered for Garth is making his midband ability cost both a Skeleton and $1 to draw, but that might be unnecessary with the level adjustments. The idea came from my belief that Black makes it unusually easy to spring back from a card deficit. Thoughts?
Blue Starter

- Redesign Lawful Search to be a $0 upgrade with “(1), Sacrifice Lawful Search to draw a card, then choose one: Look at an opponent’s hand. Look at an opponent’s discard pile.” and “When Lawful Search leaves play, draw a card.” This would give Blue a 50% chance of being able to determine if a hero can safely be played on turn 2 and would generally help Blue’s consistency at being able to detect and respond to threats, especially when choosing a gold value to block with Newsman.

- Musketeer could probably have 3hp or haste
Starting with the smaller of these two, Musketeer costs $2, right? The only $2 starting deck unit with 3 HP is Fading Argo, and the Fading part is the justification for that. I guess having 1 ATK to start with might be enough to balance it out, even with Long Range? Both ways should probably be tested, since it does need some kind of boost (are there any matchups where it’s not an auto-worker?)
My objection to Lawful Search as an upgrade is that it feels so clunky. Other upgrades do something passively while they’re in play, whereas this one would do nothing until you’ve paid the cost for its ability… Which sacrifices it. It’s about as opposite the flavor of an Upgrade as possible. Might I suggest instead that it remain a spell, but have a bit of text on it similar to the part of Judgement Day and Rewind that lets you play them without meeting the normal requirements for ultimate spells? Something like “This can be cast by an Administrator or Guard unit (instead of a Hero)” would allow you to use it to see if it’s safe to summon a Hero, it works with three units in the starting deck and four Law Tech units, and it’s better flavor-wise since there needs to be someone there to do the Lawful Searching, right? I decided against letting Soldiers cast it so that it doesn’t benefit [Purple]/Peace/X beyond the starter deck, since that’s a good enough combo as-is.
Law

Reduce Jurisdiction to $1 and/or add “you may either discard the spell or return it to your codex.” While the idea of being able to play Free Speech with Bigby when Quince is unavailable seems solid in theory, the $2 increase is a burden that Blue can seldom afford, and being limited to spells still in the codex is beyond awkward.
Make at least one spell, probably Judgment Day, able to affect tech III units. As it stands, Blue’s answer to tech III threats is through prevention, but it’s not competitive enough in the early and mid game to be able to do so without falling behind. Having an effective board clear would give Blue a chance to make a comeback if it loses the race to tech III.
Change Stash to read “You can set aside a card during the draw/discard step. If you do, draw 1 less card and add the stashed card to your hand during your next upkeep.” This is solely to protect the stashed card against forced discard.

- Tax Collector could be a 2/4 or 3/3 probably
- Jurisdiction could maybe cost 1 instead of 2
Both of you say Jurisdiction should cost $1, huh? That says something!
In all honesty, all of these changes seem reasonable. Law is probably the weakest of the Blue specs, so this wouldn’t suddenly break the balance of multi-color like buffs to some other specs involved here might.
Peace

- Make Boot Camp able to target Onimaru. Blue has no other way of removing -1/-1 runes from Onimaru than to let him die, and he’s very expensive to level up.
I think this might be a bad idea… Yes, it’s bad that there’s no way to remove -1/-1 runes from Onimaru, but consider two points:
- I believe the general consensus is that replacing Disease with Finesse not only makes it stronger, but arguably makes it the strongest codex in the game. Doing that removes all sources of -1/-1 runes except for Poisonblade Rogue, who can only inflict them by attacking and has 1 HP. This is the one of the few ways pure Black has an advantage over PtW.dec, and the lack of those runes without Disease segues into…
- In any matchup without access to -1/-1 runes, this would allow Onimaru to potentially grow too big to deal with, especially with The Art of War. With swift strike, readiness and unstoppable, anything that doesn’t have hard hero removal just dies if he can get big enough.
Basically, it would help against out-of-the-box mono-Black, but I’m afraid it would be too strong outside of that matchup. Boot Camp is already a very strong spell in a very strong spec, so making it better seems like a bad idea.
Truth

- Mirror Illusions feel like they could be 1/1 or 0/2 instead of 0/1 and still be fine
- Quince could perhaps replace Dreamscape / Hallucination with something that makes illusions un-poppable for a turn (stopgap until Macciatus, makes Hounds and Flagbearer a little more useable especially in this matchup, black has such cheap / convenient targeting)

I disagree with FrozenStorm’s suggestion of replacing Dreamscape or Hallucination. I think they’re both important parts of Sirus’s kit, even though I never managed to use them successfully here. Also, tech I illusions are dirt cheap, so I think it’s fair that they’re easy to dispel. Spectral Aven and Mirror Illusions are a different story, as losing one to Deteriorate is a $2 swing in Black’s favor at a time when Blue is desperate for gold, but I hesitate to buff the Aven because early flying is powerful. Maybe Sirus could create Mirror Illusions for $1 instead of $2, but I’m not sure that would be fair considering their potential power. Maybe if using his other abilities to transform them cost $1 also, it would balance out.
Yeah, replacing Hallucination and/or Dreamscape goes a bit far for a balance change, so I’d prefer to leave them alone. With the change to Deteriorate I suggested, there should be less need to change the pricing of the Mirrors. I’m not a fan of the Mirror tokens having 2 HP or 1 ATK in their base form simply because it’s bad flavor; they’re meant to be fairly useless until they’ve been transformed. Then again, considering that Garth can summon a stronger token for only 1 gold, maybe having it be $1 to summon and $1 to transform would be better? It does make it much easier to use them as chump blockers, though… Testing would be good.
tl;dr: Most of these ideas are good, I don’t know how many of them are necessary or how it would work out if several were implemented at once, but I want to test them out! Also that took most of four hours to format and add my own thoughts, wow.
@FrozenStorm, I’ve never played mono-blue and I doubt I’d reach Nekoatl’s level of skill with it (not my usual style), but if you’re willing to help me figure out how it works I’d be happy to test some of these with you!