I like it so far.
Disrupting Shoal is the best we can get for a free counterspell, but it surprisingly has been very good. Can discard Rune Snag to make it more powerful and also Spell Pierce when it's useless in the late game. Modern's curve is very low so I've been impressed with it. Also, it's one of those cards that you hard cast a lot more than you think in the late game. With Rune Snag, I've always been one of those guys where "RUNE SNAG IS WAY BETTER THAN MANA LEAK," and how it has minor synergy with Disrupting Shoal, I thought it was a very good include. Also, you play 4 or none, so that explains the decisions on the numbers. Spell Pierce is a good card. Discard later in the game if you don't need it. Good early counterspell, and think the deck needs a one mana counterspell besides Cursecatcher. Maybe not. Help me out.
I think I have all of the essential Merfolk creatures in my deck, and I don't really see a point in trying to jam a one-of Kira, Great Glass-Spinner or Coralhelm Commander, although I still may take out a Spreading Seas or something for a one-of between one, or both, of those two.
Now the 4-of Spreading Seas I realize is not a common thing to do, but I really like it. Now having 8 Lord of Atlantis, your Merfolk sure become unblockable quick with this card. Even if they destroy it somehow, you drew a card, so a 2-for-one most of the time. If your hand is flooded with them (no pun intended), you can just discard it to Disrupting Shoal or at the worst it cycles for 2 mana. Just one of those cards that's almost never dead and sometimes just screws over your opponent.
I really like the lands I have for this deck. With the 4 Spreading Seas, it tempts me to go on a bit of a LD plan, so that's why I have the 3 Tectonic Edge. I also think the synergy is cool, how Spreading Seas doesn't destroy the land, so Tectonic Edge will still probably get to a land. I have 4 Mutavault in the deck because it's one of the best lands ever printed and it's excellent in a Merfolk deck. And the Cavern of Souls is just so good in this deck. Since none of the non-creature spells have really hard blue mana cost, it doesn't hurt the mana, almost not at all. Having your Merfolk not be counterable is nice...very nice. So seems like an auto-include if your mana requirements are similar to mine. With all my play-testing, 21 lands, (10 colorless, 11 islands) seems like the sweet spot, so I just have 11 islands for said reason. I may edit around how the numbers are with my colorless lands, but I think definitely want the 11/10 ratio.
Help is always appreciated, so recommend me some cards.
Cards to consider:
Spellsnare
Remand
Phantasmal Imagine
Vedalken Shackles
Coralhelm Commander
Phantasmal Image
Kira, Great Glass-Spinner