When starting a game of Little Alchemist, one of the initial questions the player is asked is to "Select Your Alchemist." What this is asking is for you to choose an Alchemist Type which, upon making card combinations in a battle, will provide certain bonuses. From the beginning of the game, there are three main types, known as Starter Types. As of version 1.30.07 (the Arena Update), players have the opportunity to earn and equip nine more types, known as Arena Types. The choice that the player makes in starter type determines the initial deck he or she receives, the initial combos he or she knows, as well as the content of the first Basic Pack purchased.
You can change your Alchemist Type by selecting your avatar on the main screen, tap the symbol under your avatar, then select your type.