To Know Someone Better, Just Transform Into Them
After that lesson with Mary, I went back to my room while continuously casting that spell to increase my proficiency with it.
I was taking her advice in maintaining the spell for as long as I could to try and learn how to multitask my magic casting, which could allow me to do simultaneous casting of multiple magic spells too. It was really quite difficult to do and I kept losing my concentration after a while which kept breaking the [Skin Mimicry] spell.
For channelled spells like this, a normal mage would have to continuously chant to keep the magic in effect. The moment they stop or stumble over the words would cause the spell to also break apart.
They would have to make chanting this magic second nature to them so that they are able to do other things even while they chant. This would be sort of like learning and memorising the lyrics to a song to the point that you can sing them while doing other things without messing up any words.