Unless you're using Complex Breeding, there are no monster girls, just ordinary girls.
It's called "rabbit womb DNA" in vanilla game, so it most likely comes from rabbit-people.
Did you unlock the sterilizing gate? It's the last upgrade from them. It prevents guests from spreading STDs, but it also prevents them from using lube or condoms.
The only way to add or remove essence from slaves is via tentacle room upgrades. Otherwise essence changes only happen to offspring, based on the essence of the parents (and a chance to have one more or less than that). From what I can tell, it's always that the essence count of the respective parent matters, plus the types of essence of the other parent. So breeding a human with only demonic essence with a goblin that has +5 in everything, won't give you a human slave that has +5 in everything, but instead a good chance that it has +1 in one or more essences of the monster.
Interesting, I have never seen this player silhouettes in my playthroughs of the game. Could that be because of mods/cheats I am using? I have only ever seen the monsters, and the only time I have seen the figures pictured above has been for the player in the estate.
Payments only count when you are on the day before the deadline.
Vanilla: On payment day, drop the two goblins into the slave trader's sell area. Note that selling earlier doesn't count for the goal, and also note that providing monsters for repayment doesn't give you money. You'll see that it's the correct day when the monster portrait on the left side has a glowing green border.
Here's the thing: i'm playing the vanilla version, but still don't get when the payment deadline exactly is.
No, if you sell them before the deadline you get money for them. If you sell them on the day of the deadline, you just provide them to the slave trader and fulfill her demand.
The deadline is on every fifth day. This, same as how to provide slaves to fulfill the slave trader's demand, is also explained in the tutorial. I recommend reading those carefully.
