As a Thief, you are going to have the choice of advancing at level 30 to become an Assassin or a Bandit.
While you do not have to choose which one to become until you reach level 30, it is a very good idea to know which one you will want to advance to as soon as you hit level 10 so that you may spec and use your Skill Points in the correct build to help you down the road as you progress in the game.
As an Assassin, you are a quick range attacker that becomes one of the most powerful classes in the game.
While as an Assassin, you can travel the world fast and do extreme amounts of damage from afar, but the downside to Assassins is that they are very expensive to train.
You will need to spend a lot of money on an Assassin while levelling and training him but as you reach higher levels you will be rewarded.
As a Bandit, you are able to deal high amounts of damage at high levels and they cost less money to train while levelling and buying armour.
While Bandit is extremely fast and can dodge a lot of enemy's attacks, they still have to go toe to toe with their foes dealing melee attacks while an Assassin can kill from afar.
If you are tired of playing with the other Maple Story characters such as Warriors, you may want to have a change of character class and try your hand at being a thief! Our MapleStory Thief training guide has all the details for training your Thief character.