I heard that you can have an 80 card Yu-Gi-Oh deck is this true?

That's not quite true! The official rules for Yu-Gi-Oh! state that a standard deck must contain exactly 40 cards.

There are some exceptions:

* Side Decks: In competitive play, players can bring an additional 15 cards for a "side deck," which can be used to swap in cards against specific opponents or strategies. However, the main deck itself must remain at 40 cards.

* Special Formats: There are some less-common formats, like "Chaos" formats, that allow for more than 40 cards. But these are not the standard way to play.

So, while you might *technically* be able to play with an 80-card deck in some specific formats, it's not the standard and is not allowed in official tournaments or casual play.