Help What is the GX rectangle?

[sakirose]

Could anyone explain how the GX pop out piece is used?

This card

 

[CrownAxe]

its a GX marker for your once per game GX attack

 

[sakirose]

Do all decks have a GX attack?

 

[GamePhoenix]

Do all decks have a GX attack?

All GX cards have a GX attack, but not all decks play GX cards.