Most Ixalan Merfolk decks go for the Metallic Mimic and Herald of Secret Streams synergy. For those who don't want to pay $40 for those 8 cards, there are other fun Merfolk synergies to exploit.
Keep blinking and playing your favorite Merfolk cards with Siren's Ruse, Unsummon, and Storm Sculptor. Stall your opponent with blocking tricks using the same cards. Pump your unblockables with counters and swing until you win
Merfolk Branchwalker and/or Vineshaper Mystic are obvious Turn 2 and Turn 3 plays. You'll want to get them out as soon as possible in order to start blinking them.
Deeproot Waters should be played at earliest convenience to start profiting tokens off replaying Merfolk creatures like Vineshaper Mystic. If you're going to be replaying cards from your hand, you might as well create a hexproof Merfolk token too. Great synergy with River Sneak who pumps once for the creature cast and once for the token generated
River Sneak and Storm Sculptor are your unblockable hitters. Sneak will pump every time you play or blink a Merfolk creature spell, and Storm will send one back to your hand to replay next turn. These should be the targets of counters from River Heralds' Boon, Vineshaper Mystic, or Shapers of Nature
Shapers of Nature is a handy turn 3 drop that will allow you to pump your unblockables in the late game. At first glance 4 is a lot to pay for 1 counter, but by turn 6/7/8 you'll need this a mana sink as most of your creatures will be on field
Siren's Ruse is the hero of the deck. Not only is it a cheap way to blink useful merfolk creatures, but can save it from targeted removal and lethal blocking damage. Unfortunately it does not interact with Deeproot Waters. A solid offensive and defensive card
Unsummon is another way to save a creature card from removal to cast it again next turn. Cheap and reliable though not as potent as Siren's Ruse above. Since this deck has nothing in the way of removal or control for itself, we opt for a defensive strategy of saving our important creatures.
River Heralds' Boon needs no introduction and is an obvious play at any point.
Jungle Delver, while not the most valuable merfolk 1 drop in Ixalan, is a cheap creature spell to trigger Deeproot Waters and River Sneak late in the game. We choose this over Kumena's Speaker for the additional late game mana sink.
Possible Combos
