In Memoria, you may run into an exclamation point that does nothing when you press the action button. These are ghosts of five card masters whose spirits reside in Memoria. You can press the Square button to challenge them, but be prepared because they are tough.
I am not very good with the card game. I know the arrows point to where your card can attack and defend, and the letters/numbers on the card have something to do with how well it will perform in a battle. I basically won all these duels by luck; I suck at the card game lol.
There are five ghosts in all: The Master Phantom, The Defense Phantom, The Strong Phantom, The Rare Phanom, and The Dark Phantom.