The Mysterious Card, Found in the Kandorean Temple, is the first class-changing item found in The Lost Age, and opens up the Pierrot class, and a completely exclusive and new set of Psynergies. The class in itself is greatly useful where it is acquired, as many problems with Djinn distribution in this early stage in the game are bound to be stumbled upon, if one is to gather the Djinn as they find them.
A strategy commonly used with this item, is that after acquiring it, the player equips Sheba with it, as Mars Psynergies are greatly useful in this first dungeon, especially against the Chestbeater trio at the end, and Juggle is a very useful one, equivalent if not more powerful than Beam. After the first dungeon, one can then equip the card to Jenna, as outside on the world map, Jupiter Psynergies are greatly effective against everything you encounter, and Venus Djinn only being a step behind them.
The class later in the game is also very useful, as it possesses spells from each element, and many support skills.