Maximum of 3 Rule

Between your Main Deck, Fusion Deck and Side Deck, you may only have 3 copies of 1 card of the same name. here are some examples:

Example 1:


 * Harpie Lady, Harpie Lady 1, Harpie Lady 2, and Harpie Lady 3 all share the same card name, so you can only have a maximum of 3 between these card names. For example:
 * 3 copies of Harpie Lady, no copies of the other three
 * 1 copy of Harpie Lady 1, 1 copy of Harpie Lady 2, 1 copy of Harpie Lady 3, no copy of Harpie Lady
 * 2 copies of Harpie Lady 2, 1 copy of Harpie Lady 3, no copies of either Harpie Lady 1, or Harpie Lady

Example 2:


 * Proto-Cyber Dragon only shares the name "Cyber Dragon" when it it out on the field. It is not illegal to have 4 or 5 cards on the field that, by an effect, all share the same card name. So, you may have 3 copies of Cyber Dragon, and 3 copies of Proto-Cyber Dragon in your Deck.

Example 3:


 * Cards that are similar in name. For example:
 * Obnoxious Celtic Guard and Celtic Guardian have different card names.
 * Swift Gaia the Fierce Knight and Gaia the Fierce Knight have different card names.
 * Black Luster Soldier and Black Luster Soldier - Envoy of the Beginning have different card names.

In all three of the above cases, a duelist have have up to 3 of each in their deck (excluding the third example, where Black Luster Soldier - Envoy of the Beginning is Forbidden in Advanced Format and Limited in Traditional Format).