Signature card

A signature card or "Ace card" is a card most associated with a Duelist, and tends to be used in a majority of their Duels, as their most favorite card. Signature cards tend to be Monster Cards

Duelists may have more than one signature card, and there generally are connection between the card and the duelist.

In some cases, signature cards are created by their owner(s) and/or only one copy of them exist in the anime like "Elemental Hero Neos" and the "Numbers".

In Yu-Gi-Oh! 5D's, Yu-Gi-Oh! ZEXAL and Yu-Gi-Oh! VRAINS, they tend to be Synchro Monsters, Xyz Monsters and Link Monsters, respectively. Signature Monster Cards may also be called Ace Monsters.

Some video games have a similar concept known as a Key Card, in which the player selects a certain card as their "ace". Yu-Gi-Oh! The Duelists of the Roses has "Deck Leaders".

Yu-Gi-Oh! GX
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Yu-Gi-Oh! 5D's
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Yu-Gi-Oh! ZEXAL
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Yu-Gi-Oh! ARC-V
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Anime

 * Protagonists
 * Every ace monster that is Main Deck-based ("Dark Magician", "Elemental HERO Neos", and "Odd-Eyes Pendulum Dragon") has the same Level of 7.
 * Every ace monster that is Extra Deck-based ("Stardust Dragon", "Number 39: Utopia", and "Firewall Dragon") has the same property of 4, except for "Stardust Dragon" (Level 8).
 * Every ace monster's ATK is 2500.
 * Every ace monster's DEF is 2000, except for "Dark Magician" (2100) and "Firewall Dragon" (N/A).
 * Every ace monster's Attribute is either LIGHT ("Elemental HERO Neos", "Number 39: Utopia", and "Firewall Dragon") or DARK ("Dark Magician" and "Odd-Eyes Pendulum Dragon"), except for "Stardust Dragon" (WIND).
 * Every ace monster's Type is either Dragon ("Stardust Dragon" and "Odd-Eyes Pendulum Dragon") or Warrior ("Elemental HERO Neos" and "Number 39: Utopia"), except for "Dark Magician" (Spellcaster) and "Firewall Dragon" (Cyberse).


 * Rivals
 * Every ace monster is Main Deck-based, except for "Red Dragon Archfiend" and "Borreload Dragon".
 * Every ace monster has the same property of 8, except for "Armed Dragon LV10" (Level 10) and "Borreload Dragon" (Link-4).
 * Every ace monster's ATK is 3000.
 * Every ace monster's DEF is either 2000 ("Armed Dragon LV10" and "Red Dragon Archfiend") or 2500 ("Blue-Eyes White Dragon" and "Galaxy-Eyes Photon Dragon"), except for "D/D/D Doom King Armageddon" (1000) and "Borreload Dragon" (N/A).
 * Every ace monster's Attribute is either LIGHT ("Blue-Eyes White Dragon" and "Galaxy-Eyes Photon Dragon") or DARK ("Red Dragon Archfiend", "D/D/D Doom King Armageddon", and "Borreload Dragon"), except for "Armed Dragon LV10" (WIND).
 * Every ace monster's Type is Dragon, except for "D/D/D Doom King Armageddon" (Fiend).

Manga

 * Protagonists
 * Every ace monster that is Main Deck-based ("Dark Magician" and "Odd-Eyes Phantom Dragon") has the same Level of 7.
 * Every ace monster that is Extra Deck-based ("Elemental HERO Terra Firma", "Stardust Spark Dragon", and "Number 39: Utopia") has the same property of 8, except for "Number 39: Utopia" (Rank 4).
 * Every ace monster's ATK is 2500.
 * Every ace monster's DEF is 2000, except for "Dark Magician" (2100).
 * Every ace monster's Attribute is either LIGHT ("Stardust Spark Dragon" and "Number 39: Utopia") or DARK ("Dark Magician" and "Odd-Eyes Phantom Dragon"), except for "Elemental HERO Terra Firma" (EARTH).
 * Every ace monster's Type is either Dragon ("Stardust Spark Dragon" and "Odd-Eyes Phantom Dragon") or Warrior ("Elemental HERO Terra Firma" and "Number 39: Utopia"), except for "Dark Magician" (Spellcaster).


 * Rivals
 * Every ace monster is Main Deck-based, except for "Hot Red Dragon Archfiend".
 * Every ace monster has the same Level of 8, except for "D/D/D Supersight King Zero Maxwell" (Level 7).
 * Every ace monster's ATK is either 2800 ("Light and Darkness Dragon" and "D/D/D Supersight King Zero Maxwell") or 3000 ("Blue-Eyes White Dragon", "Hot Red Dragon Archfiend", and "Galaxy-Eyes Photon Dragon").
 * Every ace monster's DEF is 2500 ("Blue-Eyes White Dragon", "Galaxy-Eyes Photon Dragon", and "D/D/D Supersight King Zero Maxwell"), except for "Light and Darkness Dragon" (2400) and "Hot Red Dragon Archfiend" (2000).
 * Every ace monster's Attribute is either LIGHT ("Blue-Eyes White Dragon", "Light and Darkness Dragon", and "Galaxy-Eyes Photon Dragon") or DARK ("Hot Red Dragon Archfiend" and "D/D/D Supersight King Zero Maxwell").
 * Every ace monster's Type is Dragon, except for "D/D/D Supersight King Zero Maxwell" (Fiend).

Trivia

 * While the main character of Yu-Gi-Oh! ZEXAL has the same ace monster in the anime and manga, a different method of Xyz Evolution is used for said ace monster in each version.
 * Anime: Chaos Xyz Evolution
 * Manga: Shining Xyz Evolution