Some players are stuck around level 16 with the story line main quest in Gridania: To Guard a Guardian. I have also died like 2 times trying to kill the Black Mage or running around with his minion.
The basic things you should do on this quest are:
1. Do not agro (get to close) the Black Mage.
2. Run around (kite him if you are range dps) with the minion and try to do as much damage as you can. At some point during the fight he will give you a poison (this is the tricky part, just pay attention to it and use an antidote, which you can buy from a merchant, as soon as the poison appears).
3. At around 10% – 15% of the minion hp some npcs will come and help you defeat the Black Mage.
Some players suggest that you can get the Cure skill from Conjurer class also if you still can’t manage to defeat him.
Below it’s a short fraps, Archer POV, that shows you my run (i know the camera is not set on the minion but i was running for my life)
UPDATE: The video was removed cause it was violating NDA agreement. GG Square Enix.