Hello! This is a deck I made after looking through all my cards a few months after getting an ixalan booster box. I thought Merfolk were super cool so I tried making my first aggro/merfolk deck.
So the idea was to grow my merfolk really fast with a low mana cost. I tried to keep things simple with cards that add +1/+1 counters on other merfolk that DO NOT require tapping other creatures, paying more mana on top of casting the creature or both. This is why Kumena, Tyrant of Orazca is not in this deck. Not only do you have to place Kumena, Tyrant of Orazca( a 3 drop) on the field to get the abilities, you have to tap other creatures when the whole point of aggro is to hit fast and as strong as possible(and you generally have about 3-5 lands through out the match so choosing which mana is used for which action must be done wisely). Because of this theme, I tried to stream line it as much as possible to get cool buffs/features straight away when I cast a creature without tapping anything and without paying extra or waiting a turn.
The next idea I had was adding haste. I really liked the idea of pumping up my little merfolks to be big, but I wanted them to attack as soon as possible. By adding haste and being able to drop more than one merfolk per turn from inexpensive creatures greatly increases the speed and damage. This process is accentuated if the second creature is Lord of Atlantis and other similar creatures. Playing multiple creatures per turn is essential to perform as efficiently as possible.
The ability of casting more than one creature per turn is mostly from Aether Vile's ability. By adding another course of mana to the table allows casting of specific creatures to open secondary features like passive buffs from Lord of Atlantis or Jori En, Ruin Diver or other 3 drops. For example, playing lLord of Atlantis and then Jori En, Ruin Diver. This process will pump up your merfolks and allow to play Jori En, Ruin Diver which will then give you another draw allowing you to have more options to play even more cards. If you have enough mana after the second drop, which you probably will given the low mana cost of creatures, you can most likely play a third card whether it be a haste or another small creature that can pump up everything else or speed things up.
Additionally, cards that are not included in this deck like
Deeproot Waters
or Jungleborn Pioneer are great if you want to 'invest' at the beginning of the game given. But keep in mind the strategy is to play multiple things per turn. Side note, including cards like Kopala, Warden of Waves will slow down your opponent giving you more time for your 'investment' to reap rewards later.
There is of course one thing to keep in mind with Aether Vial. Because the counters must be equal to the CMC of the desired creature(specifically creature) you can not use it for Emblem of the Warmind. In practice, you must maintain the mindset of "aether vile must be used for casting only creatures and you lands for secondary 'ablities' or 'features'". Once you are able to segment your 'mana pools' for different resources you will able to trigger abilities/features more efficiently and earlier. This will increase your speed and chances of winning.
