So, I was thinking this might also work with "costs less for each flooded land [your opponents control]"

(I was also thinking how much more difficult Hex Parasite-like effects make the current flood mechanic)

Ugh. I didn't read CU09 Dam Break. Well, let's do what all the sets are doing these days and put Cancel in this slot.

Flood could change. I'm sorry if I seemed like I had a problem with the Aquitect's Will version of the effect, because I don't, and it would probably be more flavorful and more flexible.
Also, for a second counter spell (sets usually have at least two, right?) I had a few different ideas. The first was "Counter target spell. That player mills X, where X is that card's CMC." This could be either a blue-black gold card or a blue card, depending on what faction we wanted it to belong to. The second is Snakefoil.

Most sets have one soft counter and one hard counter at common, and some other counterspell at uncommon. At the moment this and CU09 Dam Break are both hard counters at common. How about something like , "Counter target spell unless its controller pays for each Island you control"?

(Incidentally, I think it's very, very preferable to say "each Island" rather than "each flooded land". It makes the mechanic far less parasitic, and more of a colour hoser (which is both a good and a bad thing)).

Can it be "unless its controller mills 1(or 2) for each island you control?" Blue always has some mill, and maybe we could boost it a bit for a creepy mind attack theme.

If you couldn't guess, I'm a bit bored with Mana Leak variants.

That gets a bit long in template:

"Counter target spell unless its controller puts a card from the top of his or her library into his or her graveyard for each Island you control". Any other templating offers?

Also, should I change the skeleton to make this a soft counter slot?

I don't like the "unless they mill" conditional-counter. It's like Perplex, but much worse: 90%+ of games the cards remaining in library are utterly irrelevant, so it makes for an utterly irrelevant spell. The Mana Leak template has a lot going for it: it allows the defender to play around it by being more cautious, and it's differently relevant at different stages of the game.

But if you really don't like that, the other broad category of soft counters is spells that only counter under certain circumstances. "Counter if its controller controls an Island" is the old template for Wave Burst, but we could have a "Counter target nonblue spell" or "Counter target spell with CMC <= 3" or whatever. Most simple variations on that theme have been printed, but I'm sure there are some versions that haven't.

I don't dislike it, and I'm perfectly fine with using it. I was just playing around with different options. I always forget that milling "doesn't really matter," because it always feels like it matters to me.

What about "Target player puts the top X cards of his or her library into his or her graveyard. If a spell shares a name with any of those cards, counter that spell." Or possibly it's UB, it reveals cards, and counters the one on the stack and exiles those in the library.

Obviously these would have to cost a bit more, and probably aren't common. Oops.

I like it when cardsets make the amount of cards remaining in library matter. I loved that in triple-Ravnica draft, Dimir Mill was a viable strategy (I won a draft with it at the prerelease). In a set with enough mindstrike and other ways to make it matter, that could be an interesting counterspell - and I'd love to see an environment where that's true. But it'd need to have a lot of support to not have it just be utterly irrelevant (or actively helping them if they have any flashback/dredge/etc), and I don't think we want to dedicate enough of this set to enabling mill.

The same applies to the other ideas. Induce Paranoia was relevant in its set, but it'd be a rather odd choice of counterspell for a casual deck that wasn't aiming to mill you. So I fear such a spell would seem rather out of place.

On the other hand, I guess Tome Scour and Burning Inquiry did enable a rogue M10 draft strategy with pretty much no support, so perhaps I'm wrong...

If it countered each spell that shared a name with the milled cards, would it be more relevant?
Anyway, I'm just tossing around ideas and attempting to come up with something new. This definitely doesn't need to go in the set. We do need to decide what blue does with the island it makes other than walk on them, and I considered putting them into some sort of mindstrike strategy. Consider Mind Washer.

I like mill, but I feel like several people have done a good job of designing sets with milling creatures, there's not that much to do in this one, and we have to commit quite a bit to it to make it a viable (or default!) strategy for blue, espcially if it's not helped by red and black. Opinion seems to be a bit split.

I would much rather keep flood, as it seems a lot more new, however, we probably do want a second mini-theme.

One possibility inspired by this card would be to have a number of cards that mill a little and somehow care about cards in the graveyard (probably particular ones, not just number). If they're useful even if the player isn't decked, that might catch the flavour of "agh, the horrors are eating my mind" without needing to be all-or-nothing. But that at least sometimes, someone can get enough of them to be a mill deck.

For instance, a spell with "Target spell's controller puts the top N cards of their library into their graveyard, then counter that spell if it shares a name with a card in their graveyard". Spells depending on cards in a graveyard are not normally great as the player has normally got the spell or creature once already, but it would get more powerful if you played multiple of these, whilst not being useless if you didn't.

Edit: Also, I agree there should be about a soft and hard counterspell in blue (more or less, probably plus one multicolor?) Probably one that gets cheaper based on islands (either wave burst in some form, or "1 less for each island") or one that floods, and one other, one soft and one hard, and it's not clear which way round they should be.

I agree that "unless its controller pays X" is not the most interesting, but is a reasonable placeholder -- I think it's fine to put something like that in, with a note to say "replace this with something set-appropriate when we realise what cards we're short of and/or someone comes up with a cool idea".