I like ur list.I think ur mana curve tend do be more green than blue , so try 8 forest and 6 island maybe.

2 copies of kopala are enough in my opinion, and im not a fan of kumena's speaker as it would be a maximum of 2/2.

Jadelight ranger is a must play on every green deck, for merfolk more than others. You can put 4 copies for the Branchwalker ( basically u r gonna pay one more green mana just to explore one more time, not so bad!!).

What do you tihnk about River's Rebuke ? could be a good finish if u play aggro in the early phase.

Thanks for your comment!

Creature wise, the deck leans on the green side, but as the non creatures are blue, the 7/7 seems to be enough to play as it's structured.

2 Kopala seems to be the right way, I'm probably cutting one of it in order to add another Crashing tide.

I don't like Jadelight ranger in this kind of build, as I'd rather play something like Jungleborn Pioneer to have bigger board presence.

River's Rebuke is a good card, but I don't want to take to long to close the game. Could be a sideboard card, but I don't have the slots for it.

behemoth94 Kopola kind of sucks. Think about it: they can fatal push most of your 2 drop merfolk. If you have 3 mana to pay for Kopala, they probably have 2 extra mana to pay 3 to push your merfolk.

Also, Kumena's Speaker is pretty much the best one drop, and is pretty solid overall.

I just played this deck and its creator. After 3 or 4 games (playng R/G Monsters), I can say that this deck is strong and can force you to play defensive while taking damage from unblockables against a flooded board of chump blockers, counter givers, card draw, and anthem effects. Very competitive build and absolutely viable in today's competitive standard meta.

Why not Opt?

I used to play opt, but lacked space due to the RIX merfolks that came, so I had to choose between card draw or protection. I've chosen protection. ericchen2003

Since your deck wants you to put Merfolk down maybe have a few Curious Obsession to improve cycling?

Curious Obsession does give some gas, buuuut there's no slot for it in this kind of build. The card draw/filtering comes from Branchwalker, Silvergill and Seafloor Oracle, and so far they do their job well.

A good answer to Goblin Chainwhirler is Heroic Intervention. Maybe go down 1 Crushing Canopy and The Immortal Sun for two Heroic Intervention. Also, Spell Pierce is more efficient than Negate in a 20 land deck so I would run the 2/2 split between them and cut a Shapers' Sanctuary. Another answer to the aggro decks is Aethersphere Harvester. Hope this is useful!

Oops didn't see the Spell Pierce in the main deck.

Kopala, Warden of Waves is good sideboard tech.

I was thinking on droping some crushing canopy/naturalize and he may be a good replacement for it as he's good against removal heavy matchups.

Seafloor Oracle seems nice as it can generate a lot of card advantage, but it seems too easily removable. turn 4 is a crucial turn, and it feels really bad to have oracle killed by any of the 2 cmc kill spells (abrade, lightning strike, Cast down, etc). Perhaps in the SB to get an advantage against control. Swift Warden is also good against single target removal. Blossoming Defense is amazing while still in the format. IDK how much you want to go into the counters plan, but Hadana's Climb  ^Flip could go well in the deck. Deeproot Waters seems slow as it often does not do anything the turn it hits the battlefield along with how going wide feels brutal against Chainwhirler and all the sweepers control has. Both Merfolk Branchwalker and Jadelight Ranger are phenomenal. They even see play in non-tribal decks. I highly recommend both. Good luck with the deck!