"It's SEA MAN!"
A little foray into Tropical Merfolk I started post Modern Horizons, deciding that while mono-blue had advantages against Blood Moon I wanted access to Kumena's Speaker. This was one of the best one-drops Merfolk had for a long while but I've dropped them and Cursecatcher in favour of Tide Shaper plus a couple of Mistcallers. I did also try Merfolk Windrobber as flying blockers were something the deck was sorely lacking but at the end of the day 1/1s simply don't really cut it in this format any longer and and putting cards into your opponent's graveyard tends to be more helpful for THEM. Rishadan Dockhand I found it too slow for me and didn't mesh with the aggro plan of the deck, but I may reconsider now we have Deeproot Pilgrimage. Enough people play islands for the Shapers to be 2/2s consistently, and have the upside of not needing to mainboard Spreading Seas (I found the tempo loss in playing that instead of a body having been fatal due to the increasing speed of the format).
Moving up the chain and as with most fish-folk builds we're running a hefty lord package at a very accessible 2CMC, plus a couple of utility creatures. Merfolk Trickster is an excellent card all round: the floor is that you can feign countermagic by not tapping out but still have a flash threat ready to attack next turn, while the ceiling is winning you the game by tapping their only blocker or turning off an ability. Silvergill Adept just isn't good enough any longer and neither is Kumena, Tyrant of Orazca, who is waiting to become a third Svyelun of Sea and Sky for a little more consistency. New star Harbinger of the Seas provides Merfolk with a Magus of the Moon that synergises with our Islandwalk lords so I might replace the two Tishana's Tidebinders with the full playset. While there are many potential applications there are for a Stifle on legs, they're sometimes a bit late coming down and are not great in other matches so sideboard might be a better home. Top end will be two copies of Subtlety, which I'm sure I don't have explain is good.
Force of Negation was a strong addition to the deck as a less mana-intensive alternate to Cryptic Command, especially as Vials mean that eventually we can just pay the casting cost and still keep the threats coming. Noncreature is of course a drawback but it still helps us deal with the wraths, spell-based combo and targeted removal cards which are most problematic for the deck. Flare of Denial gets around this restriction, and while it requires sacrificing a creature rather than exiling a card to cast for free given our game plan is to flood the board this is usually no problem. On top of this the card disadvantage is slightly lower as you lose something the opponent already knew was on the field rather than a card in hand. I used to have only two Dismembers in the sideboard (reasoning it didn't stand up to bigger lads like Murktides or Titans) but the format is so full of efficient small threats I've brought the other two into the main. Paying four life and one mana to cleanly answer the majority of the most-played creatures before they get out of hand feels like a good deal.
Mana base is about what you'd expect, with the LCI reprint of Cavern of Souls I'll probably pick up a few more copies but considering the hostility of the format to creatures making them uncounterable isn't a big deal compared to keeping them alive. The channel lands are great and I've found room for all four copies of Mutavault, which elsewhere seems to have fallen from favour a little bit but I still really rate with Vials and lords.
The sideboard packs a couple of Collector Ouphes and green protection spells, which have applications in my meta, plus the rest of the Dismembers and counters. Grafdigger's Cage is decent insurance against Collected Company, Kroxa and the like too.
