See the set's mechanics page for more about proclaim.

Unfortunately the must-have scry reminder takes a lot of space here. This also makes it so that there are now 3 cards in blue at common that have the mana cost of :S

One thing I have noticed is that you're giving cards that traditionally cost costs that are . Was this a conscious decision to move these effects further away from hard Blue?

For reference, I'm referring to this card (not necessarily a full hard counter like Cancel and Dismiss, but it seems close enough outside the context of this set), and Call of the Sea. Might be a good opportunity to diversify costs.

And on another note, given the now-evergreenness of Scry, I think you can arguably remove the reminder text when necessary. Compare texts for Dissolve and Jace's Defeat. On Commons, while Kaladesh commons had scry reminder text, Magma Jet in MM3 didn't, though it may be because its a Masters set.

The whole "hard counters require " has been lessened recently. It has been updated to "requires two colored mana of which one has to be blue". In any case, this is quite similar to Frazzle. I just don't really see the double being an important factor - even for hard counterspells. I think these recent updates to this policy also reflect that it isn't that important: it's more of a tradition.

As for Call of the Sea, it would be wholly pointless to make its cost more color intensive - the effect is powered by the number of Islands after all. I'm fine if someone wants to use it to gain control of a 1 power creature (or even 0 power).

Are there other cards in the set that you think should have in their mana cost?

Scry reminder: It's definitely because it's a Masters set. Didn't the first set have a storm/suspend archetype for example? That would be hiiighly unlikely to be ever seen done in a standard legal set.

I've been looking at the Proclaim cards, and the order of text has always bothered me. I have a better way, and I hope you consider making this change.

Silences Yet Unmoved

Instant C

Counter target nonenchantment spell.

Proclaim (Pay and continue play with this card revealed from your hand. Proclaim a card only as a sorcery and once only.)

When you proclaim Silences Yet Unmoved, scry 3. (To scry 3...)

First, I consider the order change to be the most important. What the spell actually does should be up front. I imagine you're basing the current template off Kicker, which shares obvious similarities, but kicker has an important difference that is the cause for that: Kicker affects the casting. As in, it must be decided when you cast the spell itself. Abilities like affect casting this way (like Flash, or "as an additional cost") are always at the front.

Proclaim is a different card mechanic; you aren't required to Proclaim at casting. As well, Kicker is always an add-on effect, while in this set you use Proclaim as both a "when you proclaim" or as an add-on effect.

Putting Proclaim after the main effect will be in line with WotC's templating, which you can see in cards with Transmute like Clutch of the Undercity.

Secondarily, you'll notice I inserted a couple words in bold. That's because when I first read Proclaim, it was unclear what it did -- that's a very bad sign. (I imagine you've likely overridden that reaction in your mind since you're so familiar with the set.) But for new players, you want things as clear as possible.

I know you want to save space, but they are both very important. Continue clarifies that you're not playing the card right now. (This is super important for someone reading the card for the first time. My 1st time I read it, I understood it meant to play the card right then, only to discover otherwise as I continued reading.) And your hand follows proper Magic templating, like Telepathy.

Lastly and specific to this card: This is too powerful and too complicated for common. It fills out 8 lines of text in my MSE. But just as importantly - this is effectively 2 spells in one. An instant speed Scry 3 for U as the main attraction, with a good splashable counterspell for 3U later. It's all just too much for common. At uncommon, it's exciting.

darnit, forgot one more thing about Proclaim:

Proclaim this card only as a sorcery and once only.

extra commentary: Normal templating rules would say "only once per game." but I believe that it's acceptable shorthand to say "once only" or "only once" for brevity. Also because it less confusing for players that you can Proclaim again in the cases that you use an effect like [Weary of the World] to move the card's zone and get it back into your hand.

For this card specifically it might make more sense to have the spell's effect first then proclaim, but for cards like Appointed Return or Coming of the Firstborn it would definitely not since those function quite literally as 'delayed kicker'.
For consistency, I think I keep the proclaim first. Also, unlike transmute, cycling, or whatever, those effects are done instead of casting the spell. Here, if you want to proclaim you always have to do so before casting the spell itself.

That continue is a really good idea, I'll have to see to changing that.

On power level:
Counterspells are especially sensitive to mana cost adjustments. This is why Counterspell is so much stronger than Cancel and why Mindstatic is 'hot carbage'. The scrying part is at sorcery speed, since that's a proclaim restriction. Keeping up 4 mana to counter something just isn't feasible unless you're ahead in boardstate. Proclaiming this makes it even worse btw, since now opponents know to play around it.

I've gone through two six-man drafts with this card as it is and I can tell you that from what I could gather out of those sessions, this isn't even particularly powerful. That might be in part because the general power level is quite high in this set, but that is the power level which the power of each individual card should be compared against anyway.

The eight lines of text is irritating, but it's a scenario similar to Galvanic Alchemist or Necrobite. Reminder text doesn't count for 4 or more lines for redflagging purposes.

Removing the scry reminder text might have to considered, but at common - unless it's a masters set or whatever - scry has always been accompanied by a reminder text. Replacing the ability with another is a possibility though that would likely push it to 4 or more lines.

This looks so much better!

Also I mispoke earlier on the instant-speed Scry. I'm not sure what I was thinking.

I think this will work okay as a very strong common. And it's good to have some of those.

I still advocate editing the proclaim text to "and continue play with this card revealed from your hand.", but I understand if you choose not to. I know you're changing normal templating like mill/bury and a few others elsewhere in the set.

Reminder texts cut a lot of corners when there's a need to lower the text length. Ie. Cascade, emerge, and the like. Those "card" and "your" words aren't crucial here since they're implicit.