The fundamental idea is to abuse Urianger and Leyak in tandem to allow you to play both proactively and reactively at the same time, all of the time. You can swing with almost all of your Forwards and tap out every turn while still retaining the ability to play powerful reactive cards like Phoenix (Hero and Legend) and Diabolos. Phoenix revives your Urianger, and Urianger will bring back the Leyak, completing a cycle and usually netting you a combat trick, Forward removal, or just allowing you to push for damage aggressively another turn. This opens up a combo-control playstyle new to Final Fantasy TCG, and is very exciting.
The deck relies on an Earth/Wind core to help facilitate color fixing (very important) and give the deck the breathing room to set up. Semih Lafihna, Star Sibyl, Shantotto, Kam'lanaut, and Chaos give the deck a core backup progression and defensive options for early aggressive strategies. Dadaluma and Barbariccia give the deck some mid-level removal, both comboing very well with Cactuar, which assists in ping damage that can be piled on multiple instances with Leyak.
The final piece of the puzzle is our good old friend Rikku H. Without Rikku H, we will lose on deck out a pretty good amount of the time. We do a lot of drawing and searching (see Star Sibyl, Kam'lanaut, Kefka, Leyak) and go through our deck at a pretty aggressive deck. But, since we leave our mana open a lot of the time and play a reactive game on the back of Leyak, we can force our opponent to go to deckout a pretty good amount of the time, and mill 2 or 3 cards in a single turn fairly often.
Living to your combo is your biggest priority in the early game and midgame. You'll often find that this is where Dadaluma earns his 3-of, since he can keep attackers at bay for a turn or two while you continue to develop backups, or even clear Forwards and put in you a small lead if you've developed Cactuars. You'll also want to find your color-fixer either by playing a Shantotto at some point or Kam'lanaut searching out your Chaos. Getting to 5 backups with a color-fixer is your biggest priority. It is almost never a mistake to forgo otherwise important combo pieces like Cactuar, Phoenix, or even Calbrena to get your 4th and 5th backups down 1 turn sooner.
If you've successfully weathered the storm you should be sitting on 5 Backups, with 3-5 cards in hand, and hopefully have a Forward (or Calbrena) and a Cactuar (or two). Obviously we won't have all of this every game, but this is the kind of boardstate we hope to achieve by the time we have about 25 cards left in deck. This is when you can really start playing the game the way you want to. At this point, Calbrena represents an eternal attacker/blocker against most matchups and can be paid for as both every time we Leyak.
As long as you have a Leyak out you can tap out every turn developing Forwards, activating Calbrena, removing opposing Forwards with a proactive Phoenix, milling with Rikku, or re-tooling your Backups. If you don't, you can often make a small play (develop another Cactuar) and simply pass the turn, content to get a little bit closer to deckout with a Rikku mill on an unchanging boardstate that they are forced to be the aggressor in. Put in a list of options like this, it may feel like the combo portion of the game is the easiest, and while it certainly can be (especially when you crush midrange matchups with a massive card advantage) it can also lead to some of the most painstakingly complex boardstates I've ever experienced in Final Fantasy. Dismantling a Mono Water Monster board or trying to play around Hecatoncheirs in the Mono Earth matchup can be really complex when you're dealing with incremental damage over multiple Leyaks with Diabolos or Phoenix, and requires a lot of forethought. Now that I've sung the deck's praises, let me talk a little bit about some of the things you wanna look out for if you're playing this deck or find yourself paired up against it.
The deck has many active components and while that serves in making it a force to be reckoned with, it also means there are a lot of small things that can be pretty irritating to play around. First of all, you're relying heavily on recurring cards from your Break Zone with Phoenix and Urianger, meaning that Yuna H and potentially Enuo can really a blow a game out even if you're being careful with your Leyaks. Additionally, Cactuar pings backed by Barbariccia, Dadaluma, and Diabolos are pretty crucial, meaning that elemental boosters and Minwu can block a lot of your pseudo-removal. Our natural counter-measure for this is Archer, but it's still something you should keep in mind when you play matchups with Minwu.
While it seems innocuous enough, instant speed removal (like Magus, Cactuar pings, or Tonberries) on your Urianger mean that you won't control a Scion when Urianger resolves, so his effect will fizzle. This can be particularly annoying and is probably one of the easiest counterplays available against the deck, so it is important to keep in mind on both sides of the matchup. As a couple of small particular cards to look out for, The Emperor can turn off about 70% of your engine and Clione can shut off the remaining 30%, so keeping multiple Summons to fight through the duo is very, very important.
I've received quite a few quips while playing this deck on OCTGN over the past week or so, a good chunk of which boil down to "this deck loses so hard to Minwu" when I clear a board with ping or "The Emperor shuts off the entire deck" when I mill someone out and Calbrena every turn. These are fundamental misunderstandings of the deck's weaknesses and are just easy excuses to make when you lose in a particularly frustrating fashion. The Leyak Mill deck's primary strength lies in it's versatility against a variety of strategies and ability to adjust to the meta. If the meta revolved around strategies that play Minwu and Yuna-H we could easily add in Hecatoncheir over the Asura and the 3rd copy of Cactuar to help mitigate those matchups. If The Emperor was a staple in every deck we could switch over to a more Lightning-heavy version of the deck with Odins and Raidens instead of Diabolos, or simply splash a couple copies of 4 CP Bahamut.
I want to note that I don't think that this deck is without weakness, just that the weakness seems to be fundmentally misunderstood by intermediate players. The deck's single biggest weakness is that it's a multicolor deck. Sometimes we struggle to stabilize against aggressive strategies like Shelke, Chocobos, and Lightning/Fire Haste because there are a limited number of turns to draw Star Sibyl and Shantotto. Sometimes we play against Opus 3 Edward and are forced to discard cards every turn. Sometimes we draw all of our off-color cards and we brick. If we play Bo3, sometimes our opponent is going to slow play and we will get a double loss. These things are the deck's true weaknesses. As builders and pilots we should keep in mind cards that can potentially shut off parts of our deck, but we should not list those cards as blanket reasons for why this deck (or any other for that matter) can or cannot be played competitively. They are just obstacles to work around when tweaking our lists or in any particular game.
