Good Morning Nax, Certain pets have moves that are linked to a mastery like slashing,wrestling, etc.. Well since Masterys on a pet are counted as a school of magic you can give it another school of magic and it removes them along with the moves tied to them.. freeing up 1-2 options for you to add to the pet... Hope this helped mate.. should ya have anymore question feel free to post or message me.. until then have a delightful day.. =^-^=