Illegal

If a card is Illegal, it means is cannot be used in the official card game at all, not in tournaments, not anywhere the only exception to this is friendly duels where both duelists agree on the illegal cards in question in terms of their effects. So far, these are the only illegal cards:

English

 * King of Destruction - Xexex
 * Obelisk the Tormentor
 * Armament of the Lethal Lords
 * Ulevo
 * The Winged Dragon of Ra
 * Meteo the Matchless
 * Queen of Fate - Eternia
 * Slifer the Sky Dragon
 * Testament of the Arcane Lords
 * The Seal of Orichalcos
 * Horakhti the Creator of Light

Japanese

 * Black Luster Soldier (normal version)
 * Fiend's Mirror (normal version)
 * Masahiro the Dark Clown
 * Super War-Lion (normal version)
 * Tomohiro the Mountain Warrior
 * Yasushi the Skull Knight
 * Zera the Mant (normal version)