So Tuvasa. Not really the Bant Merfolk we wanted but.... is it the one we needed.
So Merfolk running White provides much needed support that Merfolk really need.
Lords: Merfolk throughout all deck build styles depend on playing lords to buff all other fish, make them big, give them evasion, and turning them sideways. Sure with the Kumena decks, who try to take advantage of +1/+1 counters and abusing tap-untap strats, at heart its really about getting fish and knocking out your opponents with said fish. Weakness: Lords are creatures and usually die. White provides much needed anthems that can also do more then just buffing your team: Heliod's Spear, Marshall's Anthem, Mirari's Wake. Anthem effects that also have an added effect that you want, removal (while conditional still removal that can deter opponents), recursion with Marshall, and Mana Doubling. And thats not all. Also there is Curse of Predation and Cathar's Crusade to put +1/+1 Couters on your creatures. AND if thats not enough value, you can use your merfolk with enchantments like Bident of Thassa and Kindred discovery to draw more cards. AND, your merfolk can permanently tap things with Glare of Subdual or Opposition, or bounce things when you cast merfolk with equilibrium. Enchantments are inherently harder to get rid of. So these "Lords" will stick around usually.
The other thing why i would choose Tuvasa over Kumena, Tuvasa gets you easy card draw by playing cards that will support your fish to draw more cards to play more support or fish. Play Tuvasa turn 2 or 3, play an Oblivion Ring turn 3-4 , remove something, draw a card. Combos that require enchantments that also draw cards are great. While Kumena can be abused a lot more for card draw and whatnot, Tuvasa at least can get you card draw on an empty board, play a enchantment that effects the board and draw a card that can help you get back in. Now you are limited to 1 card per turn, putting Leyline of Anticipation and flash enchantments will help draw a couple extra cards. Also, usually you are committing cards to the board that are harder to get rid of, so fish die, enchantments usually stay.
Enchantments are strong, playing them to get you enough value, then making your creatures strong enough to attack is pretty good, but if that doesn't work, there are some combos to help you finish out the game. One of the more noticeable things you can do is unlimited Mana and unlimited Merfolk Tokens, all you need is Intruder Alarm+Cyrptolith Rite (or Song of Freylise)+ Stonybrook Schoolmaster or two other merfolk+Summon the School. You swing in next turn with 100+ Merfolk wizards and win. Now you can also keep up constant counters with Intruder Alarm and Lullmage Mentor and 6 other merfolk which could happen. Drowner of Secrets is a way to mill opponents and win that way. A more degenerate way of making everyone unhappy is by bouncing their entire board with Surgespanner to make sure all your merfolk will get in next turn.
Basically, play enchantments, use said enchantments to give Merfolk abilities and value, play Tuvasa, draw cards, win.