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Deck Building Theory

TCG Deck Construction Theory and its Application to Duel Links

To preface this writing, it must be known that this theory is based on Patrick Hoban’s Ideal Deck Curve Theory, which is talked about at length in his book, Road of the King. I will be adopting some ideas from it here, such as the ideal deck curve which is not one of my own findings. It is important to note that much of Road of the King is not applicable to the TCG anymore, and especially not applicable to Duel Links because of the inclusion of skills and the changing card roles. What I will be contributing to here instead is applying these theories and concepts to Duel Links in a manner that traverses formats.

First, I will explain the deck curve theory. The concept involves the theory that there is a specific range of card roles that are accepted in a “perfect deck.” The idea of a perfect deck can only be achieved in a vacuum as there is a perfect deck for every tournament, but this theory can get us as close to it in a vacuum as possible. Using these rules of thumb, we can create a deck with the ideal level of balance between each of our cards. When a deck is referred to as being unbalanced or built poorly, we can compare the list in question with these general guidelines. The decision on whether the curve is balanced or not is based on our game plan, the card roles to achieve that game plan, and the fluff we include in between.

Next, let’s discuss card roles. This, in my opinion, is by far the most important concept to understand when it comes to deck building theories. Every single card in your deck will adhere to one of the following roles: starter, extender, defensive, bomb, removal, and engine requirement. These are the roles that are present in Duel Links. Let’s define them so we have a greater understanding.

  • Starter: the best cards in your deck that allow you to push forward towards your game plan, either alone or with non-specific cards
  • Extender: the cards that support your starters to move forward towards your game plan, but rely on you or your opponent to make other plays before they become useful
  • Defensive: cards that exist solely to lower your opponent’s power ceiling
  • Bomb: a card that can be potentially game-ending on its own, sometimes high-cost or usable late game
  • Removal: cards that eliminate specific threats

Every card in Duel Links will fall under one, or often times many, of these categories. If a card fulfills multiple roles then it eliminates the need to have as many of those roles, but every card is primarily one role in regards to the game plan of the deck. Let’s take the stock KC Cup Elementsabers deck list in the game to use as an example for how to classify the card roles.


Elementsaber-Invoked

Main Deck: 20 Cards

  • Starters: 9
Duel Links Card: Aleister%20the%20Invoker
Duel Links Card: Aleister%20the%20Invoker
Duel Links Card: Aleister%20the%20Invoker
Duel Links Card: Cosmic%20Cyclone
Duel Links Card: Cosmic%20Cyclone
Duel Links Card: Cosmic%20Cyclone
Duel Links Card: Palace%20of%20the%20Elemental%20Lords
Duel Links Card: Palace%20of%20the%20Elemental%20Lords
Duel Links Card: Palace%20of%20the%20Elemental%20Lords

Note: Cosmic Cyclone (only because of Sorcery Conduit, otherwise this would be a removal card)

  • Extenders: 9
Duel Links Card: Elementsaber%20Molehu
Duel Links Card: Elementsaber%20Molehu
Duel Links Card: Elementsaber%20Molehu
Duel Links Card: Elementsaber%20Lapauila
Duel Links Card: Elementsaber%20Malo
Duel Links Card: Elementsaber%20Nalu
Duel Links Card: Invocation
Duel Links Card: Invocation
Duel Links Card: Elemental%20Training
  • Defensive: 2
Duel Links Card: Treacherous%20Trap%20Hole
Duel Links Card: Treacherous%20Trap%20Hole
  • Bombs: 0

  • Removal: 0

Our starter cards here are the game plan. They work without needing to open another specific card. Our extenders may seem like they don’t belong in that role because they are mostly monsters, but we rely on those monsters to already exist before we use Invocation, and they are necessary for us to “extend” our plays. Take note of the fact that there are no removal cards and no bombs. In any other deck, Cosmic Cyclone would be removal, however, it’s primary role here thanks to the skill is to allow us to draw Aleister the Invoker, the most important card in our deck. Take note that Elementsaber Molehu would also both fall under Extender and Defensive, but it’s role is primarily Extender. A bomb does not exist for this deck because we have delegated that role to Invoked Purgatrio. Any time that we can, we should always dedicate a role to the Extra Deck if it’s possible without compromising on our list. Any card in the Extra Deck is searchable and that’s ideal. An example of a bomb card in the current meta game would be The Eye of Timaeus. Eye is a card that is great late game and can potentially end the game in an instant, but it’s difficult to always use and not ideal when you aren’t ending the game so the Dark Magician deck doesn’t play too many of them.

Where do these roles come into play with the ideal deck curve? This is where the concept of balance comes into play. Patrick’s proposed ideal deck curve is an excellent example that he has used in every deck list he has seen competitive success with. Through rigorous testing he provided the following theory based on a 37 card TCG deck.

  • 11-13 Starter Cards
  • 12-14 Extenders
  • 3 or fewer Removal Cards
  • 6 or fewer Defensive Cards
  • 2-3 Bombs
  • 1 or fewer Engine Requirements (bad cards that must be played. An example is Elemental HERO Neos.)

Now how do we convert this curve to Duel Links, a game with 20 cards in the deck? We find these ranges using a hypergeometric calculator to determine the percentages of opening 1 card with these specific roles. The following curve is a percentage based curve involving the chances of having 1 of the cards in your opening hand while going first (0.9000 = 90%).

  • 11-13 (0.8491 - 0.9025)
  • 12-14 (0.8781 - 0.9228)
  • 6 or fewer (< or = 0.6102)
  • 2-3 (0.2553 - 0.3616)

Now let’s convert these values to be relevant to duel links with 20 card decks and 4 card hands instead of 37 and 5.

  • Starter Cards 7 (0.8524) - 8 (0.8978)
  • Extenders 8 (0.8978) - 9 (0.9319)
  • Defensive Cards < or = 4 (0.6241)
  • Bombs 1 (0.2) - 2 (0.3684)

If we assume these ranges depict the ideal deck curve in Duel Links, we can already draw some conclusions from the deck list given earlier. We can see that there is 1 more starter than generally accepted and this may suggest that the ideal number here is not 20 but perhaps 22 cards is correct. Let’s add 2 more defensive cards for a total of 4 defensive cards in this deck and calculate the new ratios.

  • 20 Cards

    • Starter Cards: 9 (0.9319)
    • Extenders: 9 (0.9319)
    • Defensive cards: (0.3684)
  • 22 Cards

    • Starter Cards: 9 (0.9002)
    • Extenders: 9 (0.9002)
    • Defensive cards: 4 (0.5817)

Looks a bit more balanced doesn’t it? Clogging the hand with multiple copies that share roles is a very real issue when building the deck and we cannot oversaturate the opening hand with the same type of card. Even if these numbers don’t look very different to you, do some test hands and feel the difference that this will make in your opening hands. Here we have my proposed ideal number for the deck with these cards that are in the in-game deck list and we improved it by adding more defensive cards. However, this isn’t always correct. Defensive cards do not allow you to further advance your game state and they only serve to lower your opponent’s ceiling, so we want to make sure we have the right number so that we aren’t the ones that can’t play the game. How about adding more cards to counter That Grass Looks Greener? Well this is not the correct way to build the deck. We should not make our deck worse in order to fight against a specific card unless the majority of the players in the game are expected to use that card. This is not the case by a wide margin.

The new proposed list I have presented is based on some ideas that could change. For example, it assumes we will always play 9 starters. Perhaps only 2 Aleister the Invoker is correct in the future and if so, we wouldn’t need 22 cards but instead we’d have 20, maybe with cutting a Elementsaber Molehu and Aleister the Invoker to maintain our ideal curve. This curve is intended to serve as a general guideline for building decks but the meta shifts and requires adding removal sometimes, such as playing Cosmic Cyclone in Dark Magicians. Let’s try calculating the deck curve of the latest pinned deck list in the Discord channel and see how it holds up to our theory.

  • Starters: 9 (0.8561)
  • Extenders: 8 (0.8119)
  • Defensive: 8 (0.8119)

Not quite as great as we thought is it? The defensive cards are too high to guarantee that we can play the game almost every time we queue up for a duel. The chance of having a bad mix of roles in the hand isn’t as low as we’d like here. Granted, this player is clearly a good player for winning the tournament and RNG was on their side, but I believe we could’ve made their deck better.

Let’s try creating curves for other competitive decks as well so that we can get a better understanding of how to properly classify these cards. Each of the following decks will be taken from the most recent pinned posts from their respective Discord channels.


Dark Magician

Main Deck: 20 Cards

  • Starters: 6
Duel Links Card: Magician's%20Rod
Duel Links Card: Magician's%20Rod
Duel Links Card: Magician's%20Rod
Duel Links Card: Dark%20Magical%20Circle
Duel Links Card: Dark%20Magical%20Circle
Duel Links Card: Dark%20Magical%20Circle
  • Extenders: 9
Duel Links Card: Magician%20of%20Dark%20Illusion
Duel Links Card: Kycoo%20the%20Ghost%20Destroyer
Duel Links Card: Dark%20Magician
Duel Links Card: Dark%20Magician
Duel Links Card: Dark%20Magician
Duel Links Card: Illusion%20Magic
Duel Links Card: Magician%20Navigation
Duel Links Card: Magician%20Navigation
Duel Links Card: Magician%20Navigation
  • Bombs: 1
Duel Links Card: The%20Eye%20of%20Timaeus
  • Defense: 3
Duel Links Card: Fiendish%20Chain
Duel Links Card: Treacherous%20Trap%20Hole
Duel Links Card: Treacherous%20Trap%20Hole
  • Removal: 1
Duel Links Card: Cosmic%20Cyclone

Blackwings

Main Deck: 20 Cards

  • Starters: 5
Duel Links Card: Blackwing%20-%20Simoon%20the%20Poison%20Wind
Duel Links Card: Blackwing%20-%20Simoon%20the%20Poison%20Wind
Duel Links Card: Blackwing%20-%20Simoon%20the%20Poison%20Wind
Duel Links Card: Black%20Whirlwind
Duel Links Card: Black%20Whirlwind
  • Extenders: 11
Duel Links Card: Blackwing%20-%20Bora%20the%20Spear
Duel Links Card: Blackwing%20-%20Bora%20the%20Spear
Duel Links Card: Blackwing%20-%20Zephyros%20the%20Elite
Duel Links Card: Blackwing%20-%20Gale%20the%20Whirlwind
Duel Links Card: Blackwing%20-%20Gale%20the%20Whirlwind
Duel Links Card: Blackwing%20-%20Gale%20the%20Whirlwind
Duel Links Card: Blackwing%20-%20Kris%20the%20Crack%20of%20Dawn
Duel Links Card: Blackwing%20-%20Kris%20the%20Crack%20of%20Dawn
Duel Links Card: Blackwing%20-%20Kris%20the%20Crack%20of%20Dawn
Duel Links Card: Blackwing%20-%20Oroshi%20the%20Squall
Duel Links Card: Blackwing%20-%20Jin%20the%20Rain%20Shadow
  • Defense: 3
Duel Links Card: Forbidden%20Lance
Duel Links Card: Forbidden%20Lance
Duel Links Card: Blackbird%20Close

Note: Forbidden Lance (unique card that acts as a way to raise your own ceiling, similar to a removal card, but because it can also serve a defensive role and depends entirely on your opponent’s actions, I’m classifying it here as defense.)

  • Removal: 1
Duel Links Card: Hey,%20Trunade!

Keep in mind that roles change depending on what your final game plan is. The way every deck wins is different, with Elementsabers amassing resources to build for a lethal swing with Invoked Purgatrio. Other examples would be Dark Magicians controlling the board until they can swing with Dark Magicians, and Blackwings trying to push through solid defenses to force their way to victory with threatening Synchros. As it stands I truly believe this theory is still true at the time of this writing in Duel Links and, no matter what deck we play, we can create the perfect list. If you’d like a more in-depth analysis of this concept in regards to the TCG, I recommend reading Patrick’s book, Road of the King. If there’s one thing to take away from this, understand there is always a mathematically correct number of cards in the deck. It’s your job as a duelist to find it.


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