"Buddy" (バディ Badi) is a special property to use monsters during the game. Before the game, players choose 1 monster from their deck and places it into the buddy zone, and that monster and all cards with the same name will be his/her buddy for that game, even if any effects change the card in the zone.
- The card used as "buddy" is not part of the 50-card deck.
- The card used as buddy does not count towards the "max-4-copies" rule.
- Players can have the 5th copy of a card they intend to use as a buddy; 4 in the playing deck, and the last one in Buddy Zone.
- At the start of the game, Buddy Monster chosen will be placed in "Buddy Zone", face down.
- When the game starts, turn the buddy face-up along with the flag, and place it in the Buddy Zone as [Stand].
- Any card with the same name, originally or changed by effects, will be treated as they player's "Buddy".
- They are always your buddy, even if not called through "Buddy Call".
- They are always your buddy, even if any card effects change the card there to a different card.
- Japanese: バディカール (Badi Kōru)
If the player would call a monster from anywhere with the same name as his/her buddy while it is [Stand] in the Buddy Zone, the player may perform a Buddy Call to gain "Buddy Gift".
- When a Buddy monster would be called (normally from hand or due to card abilities), instead of placing the monster card directly onto the field.
- The player puts his/her [Stand] card in the buddy zone to a monster area. Paying any [Call Cost] if called by normal mean.
- The player places the card originally intended to be called to the Buddy Zone as [Rest]. That card stays there as [Rest] for the rest of the game.
- If the call is successful, the performing player gains 1 life with "Buddy Gift" (バディギフト Badi Gifuto)
Thus, players are generally limited to one buddy call per game. Unless the card in the buddy zone somehow [Stand].
Some non-monster cards can also be used as buddy. In such case, that card must explicitly state in its text that "This card can be your buddy". In such case, the card may be used in a similar manner to Buddy Call, and buddy gift may be gained.
Currently, this mechanic of "non-monster buddy" are only found on Item cards.
- Main article: Lost World
If a card chosen as a buddy is a Lost World card, the card remains face-down in the Buddy Zone until the "Lost World" is played.
Players may also have multiple buddies if an ability allows so. In such case, all cards chosen as buddies due to the ability will be regarded as the player's buddies, and can be buddy called separately.