The black knight

There once was a mage with quite the potential power, but what he lacked was a student to continue his teachings. So he searched a nerby city for potential students

...

Finds three who are interested.

Put them to a test, but the slowest and least witty wins and so he takes him in.

The urchin finds a bound wizard in the dungeon he is not allowed to visit and---

Caged Mage that asks for water, that foolhardy persson gives untill the mage brakes free, but grants a small wish as a return of favour.

The favor is used to defeat the dark night that was broken free and he is so made full wizard.