Magician

Magician 1st Job Advancement (Requirement: Level 8, with 20 INT)
Go to the Magic Library which is located at the highest point of Ellinia, where you’ll meet up with Grendel the Really Old. Talk to him and he’ll advance you as a Magician if you’ve the requirement stats.

Magician 2nd Job Advancement (Requirement: Level 30)
Once you’ve reached Lv 30, go back to Ellinia’s Magic Library, which is located at the highest point of Ellinia. Go inside, talk to Grendel the Really Old. He’ll give you a letter and you’ve to pass it to the job advancement instructor located at the north of Ellinia. After giving the letter, you’ll be given an errand to collect 30 Dark Marbles by defeating the monsters inside. Be careful to stock your potions up before you start collecting the 30 Dark Marbles.
Once you’ve collected 30 Dark Marbles, talk to the instructor, and he’ll award you with a Proof of a Hero. Go back to Ellinia’s Magic Library, and talk to Grendel the Really Old once again, where then you’ll advance as the Cleric/Fire-Poison/Ice-Lightning

Magician 3rd Job Advancement (Requirement: Level 70)
Go to El Nath – Chief Residence and speak to Robeira. After talking to Robeira, head back to Victoria Island and talk to “Grendel the Really Old” which is located in Ellinia. Next, find the Door of Dimension located at Forest of Evil II and it’ll bring you to “The Path of the Glittering Crystal”. Walk until the end of the path and enter the portal to defeat the wiseman’s dark side to obtain the Black Charm.
Return to “Grendel the Really Old” and exchange the Black Charm for a Necklace of Strength. Return to El Nath after that and give the item to Robeira. Head on to the Holy Ground at the Snowfield (Sharp Cliff II). 1 Dark Crystal is requirred to answer 5 questions to obtain the Necklace of Wisdom. Again, head back to Robeira in El Nath and give her the Necklace of Wisdom.