Alchemists, without a doubt, can be a very useful class. Alchemists have the ability to mix various items you have inhand in your inventory. When they do so, it makes a brand new item that can cause even more damage or to heal a large amount of HP to party members. Basically, an alchemist can combine any type of item, and it can have nearly any effect. If you remember Rikku's overdrive from Final Fantasy X, you probably know pretty well how the mix command works.
Another great thing about Alchemists is that they can make items, meaning that when they use their command for a specific item, they it won't come out of your inventory. With their Chemist command, the healing items will also have double effect, which means they can work as excellent healers. They could be used as an alternative for a white mage - they have the attack command, have higher defense, and can heal all at the same time.
How to Obtain: You can obtain this dressphere when you complete the Clean Sweep game with Clasko in the Calm Lands. You can do this during Chapters 2, 3, and 5.