Mistress Mystique needed to punish and humiliate her slave so she did it in a way he had never experienced before. The mistress used her ass to do it and so she buried his face in her ass given that she has a big ass. He could not breathe properly and he panicked as she did it. But he realized that he had to obey her always to avoid such punishments.
Mistress Mystique does not like people who do not know how to remember things easily. She feels that such people are not serious with life and hence need to be punished. That is why she did not hesitate to trample this guy and make him lick and smell her farts. For good measure, the naughty mistress peed on the guy and he had no choice but to drink it all.