This is my brew of Merfolk with the primary game plan of going wide, with a hint of control to protect all of your lil' Merflings.
How to play this deck: (Ideal Situation)
Turn 1, play a Benthic Biomancer, or Kumena's speaker.
Turn 2, play a Deeproot Elite, or Silvergill Adept if you need the draw. Attack with turn 1 drop if there are no blockers. You can also use Biomancer's adapt ability on your opponent's endstep to get a draw if hand is dry.
Turn 3, play a Kumena, Tyrant of Orazca. Deeproot Elite triggers and place the +1/+1 counter on Kumena for future unblockable swings, or Deeproot Elite to beef him up from potential removal spells. You can attack with the other merfolks if the board is clear, or leave 3 merfolks to tap on your opponent's endstep to get a draw before your turn.
Turn 4, play multiple merfolks if you can, or save at least 2 mana to flash in Merfolk Trickster, protect your creatures with dive down, or for a bluff if your hand is dry. Merfolk Trickster should ALWAYS be played on your opponent's turn to either surprise block, tap target creature from attacking, make an opponent's creature lose all it's abilities, or if you need an extra attacker for your next turn. This will trigger Deeproot Elite and you may put the counter on any creature you want, pending the situation you're in.
Turn 5, repeat the above process, or play a Tempest Caller or Sleep to tap all opponent's creatures if there are any. Sleep allows you to keep building by keeping the creatures tapped, so this is ideal. It's ideal to wait until you have a good size board before playing a Merfolk Mistbinder from heavy removal decks. Swing with all the merf dingalings and smash face!!!
You also have Incubatipn // Incongruity for A) searching for a specific creature piece to your puzzle, or B) removing an annoying creature that would be in the way of your swing, or C) both.
REMINDER
1) Don't use sleep until your board is big enough for 2 big swings for the win.
2) Don't tap your merfolks on your turn, save that for your opponent's end step.
3) Don't play your Merfolk Mistbinder until later in the game when you need the extra boost.
4) Leave at least to bluff a flash in of Merfolk Trickster, or for Divedown to protect a Merf you need to keep.
5) Don't invest too many +1/+1 counters on a specific creature, unless you have a Divedown, Spell Pierce or Negate.
Build your Merfolk community, protect them at all costs, and go wide with your watery friends.
BOOM, you just went wide and crashed a wave of pure awesomeness that would make Aquaman proud.
