I wanted to build a deck around Kiora, Master of the Depths - a compelling challenge to make a card that apparently no one cares about work as well as possible.
My first step was to look at each of Kiora's abilities and figure out what exactly they were trying to reward you for. Untapping a creature and a land is fairly specific for a Planeswalker ability, and what benefit do you get? One extra mana? An extra blocker every turn? Possibly, but that's not what it's trying to get you to do. What Kiora's +1 really, really wants is cards like Shaman of Forgotten Ways. Instead of one extra mana, now you're getting three. It's a ramp or midrange enabler.
Okay, so we've narrowed it down to some kind of midrange or ramp deck. But those choices are narrowed down even further when we look at Kiora's -2: something that wants you to run as many lands and creatures as possible. In today's Standard environment, ramp decks run relatively few creatures, mostly relying on sorceries to build their mana base in order to drop an Ulamog, the Ceaseless Hunger. So if you start using Kiora's second ability in that kind of ramp deck, chances are you'll be milling a lot of cards you otherwise would have wanted to use. As nice as it would be to run zero instants or sorceries, however, depending purely on mana dorks for acceleration is a risky proposition. This lends us more towards a ramp/midrange hybrid, running a relatively small number of non-creature spells.
Similarly, although this is a minor point, Kiora's ultimate also rewards playing creatures by turning every huge dude into a removal spell. With that analysis complete, I had an outline for my list. As many mana dorks as I could get away with, big creatures, bare minimum of sorceries. But what sort of creatures were even available to blue/green? How far could you go?
I bounced back and forth between playing a deck that curved out at six (playing it safe) or playing a deck that pushed Kiora to her limits and ran a couple of big seven-drops on top of it. Ultimately, none of the available six-drops were good enough to be real game-enders, whereas going just one mana higher gave me access to cards like Sphinx of the Final Word and World Breaker. So I ultimately chose to go the ramp route with a slightly more top-heavy curve.
So now that you have a basic overview of the deck's general game plan, let's break it down on a card-by-card basis:
Deathcap Cultivator: The best available mana dork. If left alone, can allow me to do some very silly things, and with Kiora's -2, Delirium is possible.
Sylvan Advocate: A valuable way to survive the aggro matchups, and a solid threat as soon as you get enough land (which this deck does fairly quickly). I don't have to talk too much about why this card is good.
Shaman of Forgotten Ways: Basically a mana dork on steroids. A central piece of the deck, and competent in combat to boot.
Nissa's Pilgrimage: Essential ramp. Its lack of mana-fixing ability is occasionally worrisome, but the deck seems to pull out well enough regardless. Guaranteeing a land drop and a one-turn accelerator - I like this card a lot.
Explosive Vegetation: More essential ramp. Only three since it's a bit on the steep side, but I might bump it up to four in the future.
Den Protector: My recovery card. In case Kiora mills away any Displacement Waves, or if one of my finishers dies to a board wipe. I'm really looking to make room for these.
World Breaker: The big, obvious seven-drop. Only three copies due to his ability to recur from the graveyard (good synergy with Kiora, Master of the Depths's -2). An early one of these can seriously cripple an opponent's land-base (hopefully hitting something like a Shambling Vent), and can otherwise take out important targets like Hangarback Walker or totally shut down a Demonic Pact deck.
Sphinx of the Final Word: I feel a bit silly running this in a deck that plays so few instants or sorceries, but this is just the finisher that I want. Uncounterable, unkillable by anything short of a Planar Outburst, and a solid four-turn clock on the opponent.
Kiora, Master of the Depths: And here she is, the star of the show. I already spent three paragraphs at the beginning of this description explaining why this card is good, so to say anything more would be redundant. Anything more except to say that I'd like to master HER depths, if you know what I mean. ;33333
Displacement Wave: Putting this in was a difficult decision, but with how high this deck curves out, casting this for anything less than X=7 turns into a one-sided board-wipe in my favor. Not to mention that casting it for two clears any tokens off the table. Good synergy with Sphinx of the Final Word.
Lumbering Falls: I want to give special thanks to this card. Eats control decks for breakfast.
Sideboard:
Icefall Regent: A core piece of the deck's sideboard plan against aggressive decks. Taps down potential attackers or blockers and takes an entire turn to kill if they have a removal spell.
Guardian of Tazeem: Three more less-good copies of Icefall Regent. Good synergy with Evolving Wilds.
Gaea's Revenge: Replaces World Breaker against control, if it has the right removal. A good way to survive an Infinite Obliteration game two, and otherwise dodges things like Anguished Unmaking and Declaration in Stone that shut down World Breaker.
Altered Ego: A flexible (and uncounterable!) threat that can severely shake up a board-state. I usually end up duplicating things like Gaea's Revenge and Sphinx of the Final Word since those aren't going to be removed - possible exceptions include Dragonlord Atarka/Dragonlord Silumgar or, God forbid, Ulamog, the Ceaseless Hunger.
Island: Boarded in to replace my Wastes (since I usually end up boarding out World Breaker in aggro matchups), in order to help me cast my two-blue fliers.
Evolving Wilds: Replaces a Forest in order to further enable Guardian of Tazeem's ability.
