Legacy-folk

[CbStrad]

Legacy-folk 75 cards, 15 sideboard 19 {Island} 3 {Mutavault} 22 lands 3 {True-Name Nemesis} 4 {Phantasmal Image} 3 {Cursecatcher} 4 {Silvergill Adept} 4 {Master of the Pearl Trident} 4 {Lord of Atlantis} 22 creatures 4 {Daze} 4 {Force of Will} 4 {Spreading Seas} 4 {Æther Vial} 16 other spells Sideboard 4 {Echoing Truth} 1 {Jace Beleren} 4 {Spellskite} 3 {Kira, Great Glass-Spinner} 3 {Surgical Extraction} 15 sideboard cards

[Falcon182]

I'd suggest making it mono blue. You're really not getting much benefit out of diluting your mana base with so many duals... If you really want to have  {Swords to Plowshares} in there, run 4  {Tundra} and 4  {Flooded Strand}. If you really want to be U/W, make sure you have some basic islands in there to protect you from  {Wasteland},  {Back to Basics} and  {Price of Progress}.

[Morales]

Mono blue is diff the way to go in my opinion. I play legacy merfolks and I run a similar creature base. I also run 4wastlands because if you hit that early and they have a bad land base then it's game. Now in it sure if you've looked into these but force of will? Daze? And standstill? I run those and they tend to win games.

[Leevai420]

Daze over vapor snag.  Turn 1 vial, into daze is Merfolk 101.

[rarehuntertay]

Legacy folk usually run some form of equipment, like  {Umezawa's Jitte}, since you are also running TNN

[Dstyle1]

Remove spreading seas (this isn't modern )

Put in some standstill. It's making a comeback.

[ImTheGuy]

{standstill} is definitely the way to go. And I'd definitely put in {merrow reejery} Using it to untap your lands and lay out your hand can be very devistating.

[Leevai420]

{standstill} is definitely the way to go. And I'd definitely put in {merrow reejery} Using it to untap your lands and lay out your hand can be very devistating.

Or untap aether vial for fishy shenanigans

[ImTheGuy]

{standstill} is definitely the way to go. And I'd definitely put in {merrow reejery} Using it to untap your lands and lay out your hand can be very devistating.

Or untap aether vial for fishy shenanigans

Exactly. There are so many uses for it. I run four in my merfolk deck.

[ImTheGuy]

Here is my suggestion.
-5 {Island}
+4 {Cavern of Souls}
+1 {Mutavault}

-4 {Spreading Seas}
+4 {Merrow Reejery}

Sixteen blue producing lands is enough and you're going to want four Mutavaults.
As for the spreading seas you're going to want to spend two blue mana elsewhere. And with all your merfolk you'll have things to play. Merfolk work extremely well as a beat down without the unblockable. Plus a good number of legacy decks play islands anyway.
Also you may want to invest in fetches to thin out your deck so you draw what you want late game.
I play Merfolk myself and they are a LOT of fun.