In this guide, we'll take a look at how a deck works in Yu-Gi-Oh, including the deck size, number of cards, and the concept of an Extra Deck.
Table of contents
The Main Deck
A deck of cards in Yu-Gi-Oh can have between 40 and 60 cards. This is known as your Main Deck. Most decks in the game will not go above 40 cards to help with consistency, but some play styles, like the Lightsworn archetype or decks used That Grass Looks Greener before it was banned, can benefit from more cards.
There are 3 types of cards that can go in a deck: Monsters, Spells, and Traps. While all Spells and Traps go in the Main Deck, only some Monsters are allowed in the Extra Deck. See the next section of this guide for more info.
Some cards will ask you to excavate a number of cards from your deck. This means that you must show the cards from the deck to both players. Excavated cards still count as being in the deck until they are sent somewhere else by the effect of the card. Keep in mind that 'reveal' and 'excavate' are two distinct actions.
While Yu-Gi-Oh Monsters do have Attributes, they do not pose a restriction to deck building, as cards can be mixed and matched however the player pleases.
The Extra Deck
This is a special type of deck separate from the Main one. It can have up to 15 cards, but you can have no cards here if your strategy doesn't require it. If you're thinking "Oh, this is the deck used for changing cards in tournaments and Best of 3 games", no, that's called the Side Deck.
The Extra Deck is used for four out of the six Special Summon Monsters: Fusion, Synchro, Xyz, and Link. None of these can ever go to your hand or Main Deck, and any card that would send them there automatically sends them to your Extra Deck. Pendulum Monsters can be put in the Extra Deck under special circumstances, but they go in the Main Deck when building. Ritual Monsters are the only Special Summon Monsters who have no business with the Extra Deck.
Number of Copies of a Card in a Deck
You can have up to 3 copies of a card in your deck. This is regardless of rarity or card type. There are only two exceptions to this rule.
First is something called a Forbidden & Limited Card List, more commonly known as a Ban List. This list limits the usage of some more powerful cards to 1 or 2, if it doesn't outright make it illegal to use them in the deck. There's no rhyme or reason to how it works, you'll just have memorize it or look it up when building your deck. Each format has its own unique ban list which you can check out here.
The second exception has to do with the name of the card. Now, you're probably thinking "Wait, if two cards have the same name, doesn't that mean they're all the same card?". Not necessarily. Let's look at some Harpie Ladies.
All of these cards have the text "This card's name is always treated as "Harpie Lady".", which includes while building your deck. This means that if you want Cyber Harpie Lady, Harpie Lady1, AND Harpie Lady, you can only have one copy of each in your deck, and you can't add Harpie Lady 3 or the original.
That's the gist of it when it comes to the rules of building Yu-Gi-Oh decks. If you want to know how to use Master Duel's deck builder, you can check out our dedicated guide.