I like the simple character design, however I am not sure whether the drawing fits the context in the description. The art is nice but I don't feel the knight shows much emotion or just I can't see the knight being dissatisfied in the art, it isn't shown well.
There isn't a lot going on in the image and I do think it is a downside, since you expect the wizard's magic to be more flashy or just make the sword look a lot more weird due to the magic. Also making the characters more expressive, like the knight have widened eyes or the wizard's posture being more expressive would add a lot more personality to the art.
I know you didn't have a lot of time to work, but an idea like that could have benefited a lot more from being animated, though it certainly isn't required for your idea to be good, just what I think can make it better.