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This page contains detailed information about the rules of the Yu-Gi-Oh! card game.
Each player starts the game with 8000 life points and a hand of 5 cards. The aim of the game is nominally to reduce your opponent's life points to 0, though there are other ways to win.
Each player's turn comprises a number of phases:
- Draw Phase: The turn player draws a card.
- Standby Phase: Players take no action, but some card effects activate during this phase.
- Main Phase 1: Turn player may normal summon one monster, and play as many spell and trap cards as they wish. Any monsters on the field may be switched from attack to defense position and vice versa.
- Battle Phase: A player may attack their opponent's monsters with any monsters they have in attack position. This works as follows:
- Turn player nominates an attacking monster from his/her own field, and a target monster on the opponent's field.
- If the target monster is in attack position, the monster with the lowest ATK is destroyed. The controller of that monster loses life points equal to the difference in ATK. If both ATK scores are equal, both monsters are destroyed and neither player loses any life points.
- If the target monster is in defense position, and its DEF is lower than the attacker's ATK, the defender is destroyed and nobody loses any life points. Note: Some monsters have an ability called "Piercing" that causes damage to be dealt equal to the difference between the attacker's ATK and the defender's DEF.
- If the target monster is in defense position, and its DEF is equal to or greater than than the attacker's ATK, the attacker loses life points equal to the difference and no monsters are destroyed.
- If the opponent has no monsters on the field, the attacking monster may attack their life points directly. If such an attack is successful, the opponent loses life points equal to the ATK of the attacking monster.
- Each monster the turn player controls can attempt one attack. Unless other wise specified either by monster or spell effect.
- Main Phase 2: Turn player can play any additional spell and trap cards they wish. If they have not already normal summoned a monster, they may do so now. They may also switch the battle positions of any monsters that were not summoned and have not battled this turn.
- End Phase: players take no action, but some card effects activate during this phase. It is now the next player's turn.
There are three basic types of cards in the game - monster,
magic spell, and trap. A player may have no more than five monsters and a combined total of five spell and trap cards (other than field spells) in play at any one time.
Monster cards are the primary type, and the game revolves around battles between various monsters. Each monster has three stats: ATK (attack), DEF (defense), and level. A higher level roughly corresponds to better ATK and/or DEF. Monsters of level 4 and lower can normally be summoned for free. Those of level 5 and 6 require the player to tribute (that is, send to the graveyard from play) a monster they already control, and those of level 7 and higher require a tribute of two monsters.
Each monster is assigned one of seven attributes. These have no direct effect on the game, but many card effects specifically affect one particular attribute:
Each monster is also assigned one of 22 types; again, the purpose of these is purely to determine which monsters are affected by which effects:
- Creator God
- Fairy (Angel in Japan)
- Fiend (Demon)
- Sea Serpent
- Winged Beast
There is also a third grouping, unofficially referred to as archetypes. These are determined by having a common word or phrase in the card name, such as "Ninja" or "HERO". An increasing number of cards specifically affect monsters of specific archetypes, leading players to complain about inflexibility in new booster packs. However, these open the door to new strategies much more elaborate than the simple beatdowns of years past. In addition to the aforementioned HERO cards (which have a number of sub-archetypes, such as Elemental, Evil, Masked, etc), the largest archetypes include Archfiends, Blackwings, and Numbers.
Monsters may be played in attack mode (vertical) or defense mode (sideways). In general, only monsters in attack mode can attack.  A monster summoned by a card effect is almost always played face-up. A monster summoned normally is played face-up if in attack mode and face-down if in defense mode. If a face-down monster is attacked, it is flipped face-up and remains face-up for the rest of the game. A player may also voluntarily flip a monster face-up by changing it to attack position.
Monsters come in several varieties, denoted by the colour of the border.
Monster Card Types
- Normal monsters (yellow border) have no special abilities, and therefore have no effect on gameplay (at least, not on their own) - instead, their text boxes contain italicized "flavor text", which can be a description of the monster or offer some sort of backstory.
- Effect monsters (orange border) have special effects that change the rules of the game. There are a few named classes of effect, though most effect monsters do not fall into these classes:
- Flip effects monsters are activated when flipped face-up. Usually, this class is identified by the word "FLIP" at the beginning of its text.
- Toon monsters can only be summoned when the spell card "Toon World" is on the field, and have a significant life point cost attached to attacking. Later toons dropped the latter, and eventually the former requirements. They can attack the opponent's life points directly if the opponent has no Toon monster on the field, but must attack any Toon monsters the opponent does control. If "Toon World" is destroyed while they are on the field, they are also destroyed.
- Spirit monsters return to the player's hand at the end of the turn they are summoned. Many of these have incredibly powerful effects in addition to this rule.
- Union monsters can be treated as equip-spell cards for other (usually very specific) cards.
- Gemini monsters are treated as normal monsters while in the field or in the graveyard. Their effects must be "unlocked" by the execution of a second normal summon, at which point they gain their effects and are treated as effect monsters until they leave the field for whatever reason. (There are cards that unlock the effect without the second summoning, most notably Blazewing Butterfly's own self-tribute effect, and the equip card "Supervise".)
- Token monsters are a special variant. Their stats and effects are not written, and are determined by whatever card was used to summon them. When they leave the field for any reason, instead of going to their targeted destination, they're usually set aside in a separate pile from everything else. Tokens can be Tributed/Fused/used for Synchro summon if allowed. They cannot be used for Xyz Summon. While token cards exist (grey border), other objects like coins can be used.
- Fusion monsters (purple border) are stored in a special side area, called the Extra Deck, outside the main deck. They are typically summoned by using a spell card or other effect to send specific Fusion-Material monsters from the hand or field to the graveyard; such a summon is called a Fusion Summon, but there are other cards that allow for other methods of Special Summoning Fusion Monsters (these are not considered to be Fusion Summons.) In any case, the resolution of the Fusion/Special Summoning effect allows the fusion monster to be summoned from the Extra Deck. Fusion monsters may also be effect monsters.
- Ritual monsters (blue border) can only be summoned from the hand by the use of specific spell cards, combined with sacrificing monsters from your field and/or hand whose combined level is at least equal to the level of the ritual monster. Ritual monsters may also be effect monsters.
- Synchro monsters (white border) are, like Fusion Monsters, stored in the Extra Deck. They are summoned by sending from the field to the Graveyard an appropriate tuner monster, as well as other monsters (called "Synchro-Material Monsters") whose cumulative level is exactly equal to the level of the Synchro Monster. Most Synchro Monsters do not require the use of a specific Tuner or Synchro-Material monsters, though exceptions to this rule exist. Synchro monsters may also be effect monsters.
- Tuner is a secondary variety, which may be applied to normal, effect, or Synchro monsters. A tuner monster is required to summon a Synchro monster. Some Synchro monsters can be summoned with any tuner, some require a particular attribute or type, and some require one specific tuner.
- Xyz monsters (black border), like Fusion and Synchro monsters, are also placed in the Extra Deck. They are summoned by stacking a printed number of monsters (called "Xyz-Material Monsters") whose levels are all the same as the Xyz monster’s rank and placing the Xyz monster on top of the pile. Most Xyz Monsters do not require specific Xyz-Material monsters, though exceptions to this rule exist. Xyz Monsters do not have levels, so level-based rules and card effects don't apply to them.
- Pendulum Monsters can be used as a spell card or placed in the Pendulum zone for potential mass summoning.
Spell cards  have a blue-green border. They have various effects that change the rules of the game. They may be played face-up, in which case the effect is activated immediately, or face-down, in which case the effect is activated when the controller flips it face-up. A face-down card can be activated on the same turn it is put into play, with the exception of Quick-Play spells. Spell cards come in several varieties:
- Normal spell cards have a wide variety of effects. When the effect resolves, the card is sent to the graveyard. They are typically rather powerful, to compensate for their one-shot nature. No symbol in most media, including the real-world card game (where there is a symbol, it is a capital "N".)
- Continuous spell cards stay on the field unless removed by the effect of another card. Their effects last as long as the card is in play, though some are only activated at the controller's decision despite constantly being face-up on the field. Symbol: Infinity.
- Equip spell cards represent weapons and items that the monsters can wield; each is attached to one monster card. Most equip cards provide a stat bonus, but some have other effects. They remain in play until removed by the effect of another card, or until the monster they are equipped to is destroyed. Symbol: Plus
- Quick-Play spell cards can be activated from the hand at any time during the player's turn. If played face-down, they are the only spell cards that can be activated during the opponent's turn, but are then not allowed to be used on the same turn as they are set. They are also the only spell cards that can be activated in response to the activation of other card effects. Their effects are activated instantaneously, and the card is then sent to the Graveyard. Symbol: lightning bolt.
- Field spell cards affect the entire field, granting bonuses or penalties to all monsters of a specified type, attribute, or archetype. Like Continuous cards, Field cards remain in play until destroyed or replaced. Only one field spell can be active at a time; if one is activated when there is already a field spell on the field, the previous Field Spell card is destroyed. Field spells are played in their own zone, separate from the main spell/trap zone. Symbol: compass.
- Ritual spell cards are used to summon Ritual Monsters. To use a Ritual Spell, one must also hold the corresponding Ritual Monster in one's hand. Symbol: flame.
Trap cards are similar to spell cards in that they have effects which change the rules of the game. Unlike spell cards, they can only be played face-down, to be activated on a subsequent turn. A face-down trap may be activated at any time after the turn in which it is played. They have a pink border.
- Normal traps cards are similar to normal spell cards. When activated, their effect is immediately applied, and then the card is sent to the Graveyard.  No symbol.
- Continuous trap cards are similar to continuous spell cards. When activated, they remain on the field and provide a continuous effect (or an effect that can be repeatedly activated) until destroyed by another card effect. Symbol: infinity.
- Counter trap cards exploit a mechanic known as 'spell speed'. Basically, a counter trap can be activated in response to any other card, but the only card that can be activated in response to a counter trap is another counter trap. Symbol: curved arrow.
Winning may be accomplished in a number of ways:
- As soon as a player's life points hit 0, they lose. Causing this is the most common method of victory.
- If, for any reason, both players' points hit 0 at the same time, the game is considered a draw.
- If a player cannot draw a card from his/her own deck at any point, they lose. Some players build decks specifically to cause this; borrowing a term from Magic, such decks are called 'mill decks' in general, but a specific name is called The Empty Jar Deck, named after Morphing Jar.
- If at any time a player holds all five parts ofExodia, they win automatically.
- "Exodius the Ultimate Forbidden Lord" causes the player to win if they have all five Exodia cards in the graveyard (but only if sent there by the effect of Exodius.)
- The card "Last Turn" forces a battle between two monsters, the winner of which wins the duel. 
- If "Destiny Board" (which bears the letter F) and the Spirit Message cards I, N, A, and L are on the field in that order, the controller wins automatically. In the Japanese version, the cards spell out DEATH rather than FINAL.
- "Final Countdown" causes the player to win 20 turns after activation. This includes the turn the card is activated, and each alternation of players counts as 1. In other words, the opponent has 10 of his own moves to win, or he automatically loses.
- "Venominaga the Deity of Poisonous Snakes" gains a Hyper-Venom counter each time is inflicts damage to the opponent. When it has three such counters, its controller automatically wins.
- If a player manages to Summon "The Creator God of Light, Horakhty", they automatically win.
- In Konami Sanctioned Tournaments, you can also lose if you are given a Game Loss from a Konami Judge for any number of possible reasons, which are explained in the "Tournament Guidelines FAQ".
- You must win 2 out of 3 Duels to win a match, unless using "Victory Dragon", which wins a match if it attacks the foe directly and defeats them.
Approximately every six months (September-March), company officials release what is known as the Forbidden/Limited List, a selection of cards that are not permitted in official play, or are only allowed in certain quantities. The current list can be found here.
- ↑ One exception to this rule is the Total Defense Shogun, whose monster effect allows it to attack while in defense position. In this case, any damage dealt is equal to TDS's ATK power. The other is Elemental Hero Rampart Blaster, though its ATK power is halved and it can only attack when you're opponent has no monsters.
- ↑ Heads would be treated as Attack Position and Tails would be Defense
- ↑ The official Fusion Summon card is called "Polymerization", but there are numerous alternatives
- ↑ Such as Gravity Bind, or any Synchro Summon
- ↑ originally called magic cards, but UDE were forced to change the name to avoid them being confused with Magic: the Gathering cards; they are still called 'magic' cards in most non-English editions of the game
- ↑ Some normal traps, when activated, are considered to be equipped to a selected monster. However, these are not considered equip spells, nor is there any such class as "Equip Trap".
- ↑ This card is currently on the Forbidden List, and as such is not permitted in official play.