U/G Merfolk

To deal damage to an opponent, attack after Tempest Caller comes into play (exile it with Release to the Wind and repeat the attack next turn). It is possible use the Herald to make unblockable creature with counters. River Sneak deals direct damage to the opponent with no compromise. Tishana can be the final attack and it can be more powerful if it is used in combination with Realese to the Wind to draw twice.

The Metallic Mimic (Merfolk creature type) can be launched with every type of mana and put a counter on every creature that enter the battlefield. Deeproot Elite should helps to put a counter on each creature that enter the battlefield and to be prepared when an Herald will come. Use the River Herald's Boon to put counters when Deeproot Elite misses. Hadana's Climb helps also in this.

The Seafloor Oracle makes quicker the draw in combination with the River Sneak. Silvergill Adept also helps in drawing. The Mistbinder is a must. Use Blossoming Defence to protect a creature or to deal the final damage to a player.

Sideboard: use Walking Balista to deal damage to a player if you cannot attack your creatures.