The limits here are flexible, but as long as you aren't whipping out this magic to solve every problem by making everything up on the spot, and you take the time for him to develop the spells in character, it's should be fine. In character, he should be getting the hang out of this new form of shadow magic now, which means he can start inventing variations/different spells with it.
If you want to have him do something really huge with it you should probably ask a mod first, but as long as you have it take some time and study to learn to do new things with shadows, you have some freedom to be creative. But, like I said, if you are ever unsure it's best to just ask real quick! Essentially what this rewards represents is that you've bought permission for him to actively be cultivating the ability, and coming up with new ways to use it, instead of it being a singular spell.
ACCEPTED!
If you want to have him do something really huge with it you should probably ask a mod first, but as long as you have it take some time and study to learn to do new things with shadows, you have some freedom to be creative. But, like I said, if you are ever unsure it's best to just ask real quick! Essentially what this rewards represents is that you've bought permission for him to actively be cultivating the ability, and coming up with new ways to use it, instead of it being a singular spell.