"Good Guy" Challenge: You have to be a "good guy" who does everything "by the book". You are not allowed to kill prisoners, cannot kidnap innocents (or kill them) and cannot rape anyone, whether they belong to you or not. Elven patrols are considered innocents and cannot be attacked. You are free to purchase slaves and capture bandits as well as ask people to join you, but NO branding. Jailing is acceptable but farm is forbidden. No Umbra occupations, and no sex work unless the slave has fickle, deviant, or pervert.
The taurus girl main quest also requires additional steps. (Because Melissa implies these requirements and I'm 95% sure it used to be a requirement.) In addition to a taurus female with giant, lactating breasts, she also has to have the lab modification of multiple breasts. (Maximize nipples, develop rudimentary nipples.) Cannot use these potions: amnesia, aphrodisiac.
Must pick the good ending and also choose to save your slave.
For an optional addition, you have to fulfill the repeatable quests as closely as possible and cannot fulfill the darker quests like brothel work and untamed rich slave.