As a level 20 death mage this guy just cannot be killed, or even hurt really. Constant weaknesses and trap after trap letting you die in maybe three rounds. As death you must put up your traps and blades or you do no damage at all it seems. I tried to get help in killing him but talking to other players just seems to have them ignore you, or in some cases make fun of you.
I have done all my death spell quests, I am ice up to tower shields with two training points left. How do you kill this guy? Oh, my gear is the stuff Greta makes for you she had you running all over wizard city for.
Before we can give specific information on "the prince with the staff, we'll need the actual name of the enemy.
I suspect that you've gotten to enemies that are too tough for your level, a common problem when doing Grizzleheim on a level 20.
Grizzleheim is an optional area and (other than merchant visits for quests) isn't required to advance in the game. While you can probably do the first area (Savarstaad Pass) on your level 20, finishing Grizzleheim on a solo wizard will likely require level 45.
As far as clothes go, you've outgrown what Greta made for you. The best way to get good clothes without buying crowns is to shop at the Bazaar in Olde Town. A good rule of thumb is to search with the "Usable" box checked, then sort first by highest level (which would be 20 in your case) and then by school. That will bring up a list of school equipment for the highest level you can use.
He is prince Miru mirini or something like that in the throne room of ire in the pyramid you do all the questing in in Krokotopia. You have a boss grid thing just outside, but it goes into a whole aera, the throne room, rather then a single boss room. You have to turn the braziers red to go in.