Mystification is a process of rewriting and changing the spell pattern to be more difficult to recognize the pattern. This process requires a lot of techniques and great understanding of the spell itself in order to change the spell patterns while still not changing the result of the spell which was the reason why this process is only been used by spellcrafters of the highest orders. It puts noise and useless spell fragments into the spell pattern so it can be hard to decode the pattern. This process is similar to encryption- making the end result of the spell hard to understand.
This process is been used by mages that want their artifacts like battle related artifacts to only be used by themselves. It also made the spell harder to break because it is hard to distinguish if they do know what spell it is.