At lv10, you can venture to Kerning City and choose to become a Thief. Talk to the Dark Lord in the Thieves' Hideaway at a basement of a cafe in Kerning City, and he will advance you to the Thief class. You need at least 25 DEX. From here, you keep leveling up until your next job advancement at lv30.
At lv30, go back to Kerning City and talk with the Dark Lord. From there, you need to complete a little test that will prove you are strong enough to take the next step in your Maple career. The test involves defeating a bunch of powerful monsters and collecting 30 Marbles that they drop. Once collected, you will be given a Proof of Hero medal to bring back to the Dark Lord. He will then ask you which advancement you want to make.
Your next advancements take place at lv70 and lv120, both are feats that not many people will reach. At these points, you will need to go back to Henesey's and complete new tests.
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